How do I set how many number of rings before machine picks up call?

Make sure you've got the machine set to answer calls, and set the number of rings to four. If you need a copy, you may download the manual here.

If you have an answering machine connected to the same line as your fax:

To make sure the printer picks up incoming faxes, set Auto Answer to On, and then set the printer to pick up after a greater number of rings than the answering machine. For example, if the answering machine picks up calls after four rings, then set the printer to pick up after six rings. This way, the answering machine picks up calls first and your voice calls are received. If the call is a fax, then the printer detects the fax signal on the line and takes over the call.

If you have a voicemail feature associated to the same line as your fax:

Voice mail and fax can share the same telephone line if you subscribe to a distinctive ring service offered by your telephone company. This feature allows you to have multiple telephone numbers on one telephone line. Each telephone number has a designated ring pattern (single ring, double ring, triple ring, or double and triple ring). The different ring patterns let you know which telephone number was dialed, and which device you should use to answer the call.

If you do not have distinctive ring service, then set the printer to receive faxes manually (Auto Answer Off). This setting lets you receive both voice calls and fax calls, but works best if you use voice mail more often. You need to turn off voice mail whenever you are expecting a fax.

I hope this helps.

Should you need further assistance, please contact Lexmark Technical Support Center.

It seems that you're sharing your home phone line with your Lexmark fax machine. You can adjust the "pick-up" ring from the printer operator panel by pressing the Setup button > Fax Setup > Ringing and Answering > Pick Up On > select your preferred number of rings before the fax answers.
Please note:
If you have an answering machine connected to the same line as the fax, set the answering machine to answer incoming calls before the printer does. Increase the number of rings by a factor of 3 over the answering machine. For example, if the answering machine is set to pick up on 4 rings, set the printer to pick up on 7 rings.

If you have a voicemail feature in the same line as the fax, you may subscribe from your phone service provider for a distinctive ring pattern feature. You can program your printer to have a distinctive ring pattern and phone number for incoming faxes.

Should you still need assistance, please leave a comment to my response and I'll get back to you. Should this resolves your problem, your rating will be greatly appreciated.

Either your fax machine is set to answer on more rings then your answering machine is or you dont have the automatic answer key pushed?

Determine how many rings your answering machine picks up on and then change the number of rings to a lower amount on your fax machine. To change the number of rings before picking up the line, press the "menu" key on the fax machine and use the up and down arrows to scroll until you find the "basic fax set up" or the "advanced set up" areas. I am not sure which one will have the number of rings setting. Try looking in both until you find it.

when you see it press "ok" or "enter" get in and change the amount of rings before answering. call your fax machine to make sure it picks up before your answering machine.

This should solve your problem.

SETTING THE RINGS TO ANSWER

The unit announces the rings to answer. To change,
press NEXT or PREVIOUS. To set and go on to the next
item, press SET.
1. Press and release NEXT or PREVIOUS until the unit
announces and displays the correct number of rings
for the answerer to pick up.
2. Once the rings to answer is set, press SET to enter
the incoming message length menu.

I have a HP Officejet J6480 All-In-One and needed the answering machine and fax to be on at the same time.  I called the help line at HP and they said I needed another phone line into the home but I tried this and it worked. 
First I got a different phone number for the fax machine - they do this for no charge at my phone company. This is not another physical line into the home - it is just another phone number with a different ring - it rings 2 fast rings for the fax machine instead of the phones regular one ring. I set the answering machine built into the phone to pick up after 4 rings and I set the fax machine to pick up on 2 rings. Be sure to set it so the fax pick up number of rings are less than the answering machine pick up number of rings.  It worked for me. Hope this works for you too.

Press
function
64
set

look at the printout
look for number of rings

to set the parameter
press
function 74
set

From the main menu select the Voice Mail option in Voice mail select Ring Delay in Ring Delay you can choose the delay time before Answering Machine pick up the phone from 0 to 30 secend.Reza from Iran

try this page...
http://images.owneriq.net/download/images/9/99351467-0ae8-2444-1dd3-486419692db0-000001.png

here is the manual

http://www.retrevo.com/s/sharp+UX-B700+manual

good luck