When its engine of power 80 kW is generating full power, a small single-engine airplane with mass 680 kg gains altitude at a rate of 2.1 m/s. What fraction of the engine power is being used to make the airplane climb? (The remainder is used to overcome the effects of air resistance and of inefficiencies in the propeller and engine.) Express your answer as a percentage using two significant figures. So I'm stumped here. I need some hints on how to get started. Any help at all would be greatly appreciated. Thanks.