How much cu ft of top soil you need to cover 60 ft by 100 ft land and 4in thick?

Answer 1

12 in = 1 ft

⇒ 60 ft x 100 ft x 4 in = 60 ft x 100 ft x (1 ÷ 12) ft

= 500 cu ft

Close, but you left out the 4 in (1/12) above. You had it on the left, but you left it out on the right. That makes the correct answer 2000 cu ft.