Hey guys, I think I know the procedure, but something about my answer is wrong. Can someone post a solution for this?

A showroom for a car dealership is to be built in the shape of a rectangle with brick on the back and sides, and glass on the front. The floor of the showroom is to have an area of 500 meters squared. If a brick wall costs $1200/m while a glass wall costs $600/m, what dimensions would minimize the cost of the showroom?