How fast is the boat moving away from the lifeguard station when the distance between the boat and the lifeguard station is 150 feet?

How fast is the boat moving away from the lifeguard station when the distance between the boat and the lifeguard station is 150 feet? 9. A screen saver displays the outline of a 3 cm by 2 cm rectangle and then expands the rectangle in such a way that the 2 cm side is expanding at the rate of 4 cm/sec and the proportions of the rectangle never change. How fast is the area of the rectangle increasing when its dimensions are 12 cm by 8 cm? What is a differential? Depends on the book you read. What is a differential in our text?