Looking for length of shorter side, longer side, and optimal region (garden + borders) (area)

A landscape architect would like to design a rectangular flower garden with an area of 72 square feet is _ surrounded by a brick border 3 feet wide on two sides and 6 feet wide on the other two sides (see figure). What dimensions of the garden minimize the combined area of the garden and borders? What is the optimal area of the combined region (garden + borders}