The motor of a ski boat produces a power of 36100 W to maintain a constant speed of 15.7 m/s. To pull a water skier at the same constant speed the motor must produce a power of 37400 W. What is the tension in the rope pulling the skier?

Just remember that power P (in watts) equals force F (newtons) times velocity V (m/s). Hence F = P/V. From what you've been given you can find the force the boat must overcome without a skier - these forces may be due to things like water and air resistance, inefficiencies in the power train, etc. With a skier attached the force the boat must overcome is increased a bit, because the tension in the tow rope opposes the boat's motion. So the tension force is equal to the difference of the two force calculations.