4 inches = 1/3 foot
So the volume of that section is (150ft x 5ft x 1/3 ft) = 250 cubic feet
The whole trick to this question is knowing
how many cubic feet make 1 cubic yard.
1 yard = 3 ft
(1yd x 1 yd x 1yd) = 1 yd³
(3ft x 3ft x 3ft) = (3 ft)³ = (3)³ x (ft)³ = 27 ft³ <===
For the sidewalk project,
250 ft³ = (250 / 27) = 9.26 yard³ .
I think the way concrete contractors operate, they'll
want you to order and pay for 10 cubic yards.