How many yards to cover 30ft/40ft 4 inches deep in concrete

Unlikely salt damage - most likely the concrete was an inferior mix or was badly laid or both and there has been some water ingress with resulting frost damage.

It can be successfully patched but the trouble with patching concrete is the repair has to have a feather edge and concrete doesn't feather edge well and a cement feather edge doesn't age well at all.

To overcome this fairly common problem there are a variety of dry and ready mixed compounds designed for concrete repair that are variously reinforced with resins and/or fibres. They are convenient but quite pricey.

I prefer to use the old fashioned method and overcome the problem of the feather edge by chiseling out more of the original concrete to make a stepped edge at least an inch deep and to make the cavity a fairly even depth of at least an inch deep leaving only good secure concrete behind.

Once the cavity is prepared and free of dust, using a good quality pva adhesive, brush it well into the repair area including the stepped edge and mop out any surplus. Mix enough concrete for the patch using a suitably sized aggregate of 1/2 - 3/4 inch and add a little pva to the mix according to the instructions and fill the cavity, tamp well down, screed off level with the surrounding area and trowel the surface to a similar finish to the original.
Further brushing or trowelling might be needed later.

Find out the brand of cement then read the formula

Assuming that 20x12 means 20 feet by 12 feet, then you take the three values in feet - 20, 12, and .333 (4 inches is 1/3 foot).

Multiply these three numbers to get the cubic feet:
12 x 20 = 240
240 x .333 = 79.92
Now that you have 79.92 cubic feet, to get cubic yards you divide by 9 since there are 9 cubic feet per cubic yard.

79.92 cu. ft. divided by 9 = 8.88 cubic yards (round up to 9).

3.09 yards

To the nearest whole number, 44 cu yards.

Do you mean how many cubic yards it would require to fill a volume occupied by an area of 30 ft by 40 ft by 4 ins deep? If this is what you mean then it would require 11.1 cubic yards. Hope this helps.Sorry I can't help with the cost.

open a calculator and multiply 5280x12x..33

AC is approx. 145 lbs per cubic ft.
there are 27 cubic ft in 1 cubic yard
60 tons x 2000 = 120000 divided by 145 = 827.58 cubic ft divided by 27 = 30.65 cubic yards

square yards would depend on thickness of AC.
you can take thickness x sq ft to get cubic ft

in concrete 1 cubic yard =
4 inch thickness = 81 sq ft or 9 sq yrds
6 inch thickness = 54 sq ft or 6 sq yards

for the 2.2L OHV:
(pully 8 4 1 5 9 <-- long bolts @ 63Nm (46ft/lb)
side ) 7 3 2 6 10 <-- short bolts / 10 is the stud @ 58Nm (43ft/lb)

for the 2.4l dohc are as follows:
(pully 9 3 1 5 7
side) 10 6 2 4 8
bolts 1-8 torqued to 65Nm (40ft/lb)
bolts 9-10 torqued to 40Nm (30ft/lb)

then (either engine) give each an additional 90° (¼) turn

it's best to do the tightening in stages, you don't want to go completely tight on the first pass or there will problems and you'll get to do it all over again

If the pipes are 3" outside diameter, the displacement is 24.15 cubic yards, however standard 3" pipe is 3.5" diameter, which would displace 32.85 cubic yards. 505.32 cubic yards is correct for the total trench volume.