The find the volume of the box, you need to multiply the L by W by H. Both the length and width have been reduced by 2 x's. And the height will be just x.
A box without a top is made from a rectangular piece of cardboard, with dimensions 40 inches by 32 inches, by cutting out square corners with side length x inches. both sides are cut by x inches
The lowest time out of all of them is 10.75, so to all the 5th swimmer needs to do to win is to undercut the swimmer who got 10.75s by a 100th of a second. i.e 10.74s or faster (lower) would win.