Will i hate theese types of questions, so just guess.
Maybe 3 so 20 divided by 3= 6.66666667 (not 3)
Maybe 5 so 20 divided by 5 = 4 (works, but u must always try the other numbers to see)
Maybe 10 so 20 divided by 10= 2 (Perfect!)
So your answer is 2 rectangular prisms!
Hope my answer helped :D
