The maximum safe load for a horizontal beam supported at each end varies directly as the width and the square of the depth and inversely as the distance between supports. If 1800 lbs. is the safe load for a beam 3 in. wide and 6 in. deep and held by supports 15 ft. apart, Find the safe load for a beam 2 in. wide and 4 in. deep with supports 10 ft. apart.
(Knowledge on classical mechanics is not needed in solving this problem)