The maximum weight M that can be supported by a beam is jointly proportional to its width w in inches and the square of its height h in inches and inversely proportional to its length L in feet. (a) Write an equation that expresses this proportionality. (Use k as the constant of proportionality.) (b) Determine the constant of proportionality if a beam 4 in. wide, 6 in. high, and 15 ft long can support a weight of 3840 lb. k