Question

I need to find the volume of the cube using v=l*w*h

Answer 1

Since it is a cube, each side is the same length. Therefore, it would be:
l = (x+5)*(x+5)*(x+5)
Which is the same as
x^3 [Cubed] + 125 = L

Answer 2

3(x+5) each side is x+5 so times that by 3. Distribute the 3 to both the x and the 5 to get 3x+15.