Problems 63–70 are based on material learned earlier in the course. The purpose of these problems is to keep the material fresh in your mind so that you are better prepared for the final exam.

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?