Answer:
You want the area of the base to equal 20 ft^2
Explanation:
Volume of a cube= (L)(w)(h)
Area of base = (L)(W)
60 cubic feet is the volume we are trying to acheive. Since the volume for a cube is (L)(w)(h), 3 needs to multiply by the area of the base to equal the volume. since 3 times 20 equals 60(You solve this by dividing 60 by 3) the base needs to equal 20ft^2.