Calculus Help Please: Optimization!?

Some airlines have restrictions on the size of items of luggage that pengers are allowed to take with them. Suppose that one has a rule that the sum of the length, width and height of any piece of luggage must be less than or equal to 186 cm. A penger wants to take a box of the maximum allowable volume. If the length and width are to be equal, what should the dimensions be?