Here the side length of the end is , and the length is .

Thus, the volume is given by:

now our constraint is that the length plus girth must be less than or equal to 120. thus we must have that

now solve for , we get:

we have the largest volume when h is as large as possible, thus take h to be such that

thus, plugging this into our volume equation, we get:

now this last function is what we want to maximize. can you continue?