I'm trying to figure out the second part of this problem. I would appreciate any help.

A closed rectangular box with a square base is to be built subject to the following conditions: the volume is to be 27 cubic feet, the area of the base may not exceed 18 square feet, the height of the box may not exceed 4 feet. Determine the dimensions of the box (a) for minimal surface area; (b) for maximal surface area.

(a) The minimal surface area is sq. ft. at the side length of the square base = ft.

(b) The maximal surface area is approximately sq. ft. (round your answer to 2 decimal places) at the side length of the square base =

I was able to solve for the minimal surface area, but i'm having trouble finding the maximum.