Show how to approximate the required work by a Riemann sum. Then express the work as an integral and evaluate it. A 0.4-kg model rocket is loaded with 0.75 kg of rocket fuel. After launch, the rocket rises at a constant rate of 4 m ys but the rocket fuel is dissipated at a rate of 0.15 kg ys. Find the work done in propelling the rocket 20 m above the ground.