A landscape architect wishes to enclose a rectangular garden on one side by a brick wall costing $40/ft and on the other three sides by a metal fence costing $20/ft. If the area of the garden is 1,800 ft^2, find the dimensions of the garden that minimize the cost.
_______ft (length of brick wall)
_______ft (length of side adjacent to brick wall)
_______ft (length of brick wall)
_______ft (length of side adjacent to brick wall)