Problems 63–72. The purpose of these problems is to keep the material fresh in your mind so that you are better prepared for later sections, a final exam, or subsequent courses such as calculus.

The horsepower P needed to propel a boat through water is directly proportional to the cube of the boat’s speed s. If a boat needs 150 horsepower to travel 12 miles per hour, what horsepower does it need to travel 6 miles per hour?