Volume is the quantity of three-dimensional space enclosed by a closed surface, for example, the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains. Volume is often quantified numerically using the SI derived unit, the cubic metre.
You have to work out the area of each side. The two identical triangles are 6x4=24 because 8/2 is 4. The base is 8x5=40. The back is 6x5=30 and the top is 10x5=50. You then add them all together to get 144 ft squared.