A gearbox operating at steady state receives 20 horsepower along its input shaft, delivers power along its output shaft, and is cooled on its outer surface according to hA(Tb 2 T0), where Tb 5 110°F is the temperature of the outer surface and T0 5 40°F is the temperature of the surroundings far from the gearbox. The product of the heat transfer coefficient h and outer surface area A is 35 Btu/h ? °R. For the gearbox,