In EXCEL The key to optimization problems is maximizingminim
In EXCEL:
The key to optimization problems is maximizing/minimizing one equation, while holding another constant. In the Solver, where do you tell it which equation to maximize/minimize? Set Objective By Changing Variable Cells Subject to the Constraints Make Unconstrained Variables Non-Negative Select a Solving MethodSolution
in set objective it will tell which equation to maximize or minimize.
By changing variables cells represent the set of variables
 subject to the constraints is that by selecting the add button the two constraints of the problem can be dictated to the solver
 make unconstrained variables nonnegative means that the variables representing the measurements of the sides of the box cannot be negative
 By click on solve the solver will give you the solution to the problem

