Chapter 3 - Introduction to Graphing - 3.5 Slope - 3.5 Exercise Set - Page 196: 16

$15$ Calories burnt per minute of running

2 minutes of running burns 30 Calories. 4 minutes of running burns 60 Calories. To find the rate a runner burns Calories, divide the change in Calories burnt by the change in the time: average rate of Calories burned while running $=\dfrac{60-30}{4-2}=\dfrac{30}{2}=15$ Calories per minute.