How long is the Belt for a White Outdoor Mower, LT 5420-G?

There are a lot of variables that would cause a belt to come off.
Worn belt maybe a stretched belt, bad pulley or maybe a tentiontin pulley went bad.
Like I said there are a lot of variables but those are somewhere to start looking.

https://www.manualslib.com/download/809988/White-Outdoor-Lt-1650.html Better late than never.

Raise the mower off the floor then put the deck down on it's lowest settings. Hope that works.

PLEASE SHOW ME A DIAGRAM OF ACTUAL BELT AND PULLEY'S FOR SNAPPER LT 200, MODEL #2690441?

The rule of thumb for the routing of the mower belts is to make sure the "V" inside of belt is fitted into your pulleys. The "FLAT SIDE" outside of the belts rides with the flat side up against your idlers (lookes kinda like a pulley but is wider.) It might take you a couple of attempts to get it right. When the belt is on properly it will be nice and snug.

Good luck
roundo4

take it too a mechanic

Remove the blade bolt and blade, slide the adapter off the crankshaft. If it will not slide off, spray it with a good penetrating oil and let is soak for a bit then take a SMALL hammer and gently tap on the sides of it while pulling at the same time

raise the front of your mower up and support it with something safe like a jack stand
take the blade off
when your blade is off locate the plastic cover covering the belt and remove
now remove the belt but first remove the plastic cover on top of the mower to uncover the gearbox that turns the wheels your belt goes from the engine pulley to the gearbox pulley
you will have to work the belt off the pulley while turning the motor by hand or the same when installing the belt.
to install belt reverse the procedure.
hope this helps some

either the wire going to the transmission is not tight enough and need adjustment or belt needs replaceing