Question 427155
Volume = l x w x h
Since the floor is square, w = l, so we have {{{V = w^2h}}}
Given:
V = 128 ft^3
The thickness of the floor is 15.5 feet less than the side length, so we have:
h = w - 15.5
V = 128 = w^2*(w - 15.5)
Now we need to solve for w.
We know w must be greater than 15.5.  Suppose it is 16.5.  Then w^2*h = 272.25.
So 15.5 < w < 16.5.
Try w = 16: 128 = 16^2*(0.5) = 256*0.5 = 128
So side length = 16 ft, thickness = 0.5 ft