Luke ran 12.5 miles and 2 hours and 25 miles in 4 hours what is the constant of proportionality

In order for the function to be linear, what must m be and why? m = 22 because the rate of change is 1. m = 20 because the rate of change is 3. m = 22 because the rate of change is -1. m = 20 because the rate of change is -3.