Hi Melissa,
If topsoil is sold $18 per cubic yard, that's equivalent to $18/27 cubic feet.
The smallest amount that could be sold is 1/4 cubic yard.
The yard we want to cover is
20' x 10' (I see you have 10m not 10' but since everything else in in ft, inches, yards, I'm going to assume you meant feet not meters).
And we want it to be 4" deep. 4" = 1/3 foot
20' = 6 2/3 yards
10' = 3 1/3 yards
1/3' = 1/9 yards
The amount of topsoil needed is
(6 2/3)(3 1/3)(1/9) = (20/3)(10/3)(1/9) = 200/81 cubic yards = 2.47 cubic yards.
Since the topsoil is sold in 1/4 cubic yard increments, we will need 2.5 cubic yards of topsoil.
2.5 x 18 = $45
Now for the truck
The bed measures 80" x 69" x 20" = 80/36 x 69/36 x 20/36 cubic yards = 2.37 cubic yards.
Since the truck bed has less capacity than the amount of soil needed, two trips would be necessary.
Remember that
1 cubic yard = 27 cubic feet
1 cubic foot = 1728 cubic inches
