rate of change=change in y divided by change in x
y= 3,6,9
x= 1,2,3
The numbers chosen above are because if mike travels 3 miles in one hours then he can travel 6 miles in two hours and 9 miles in 3 hours.
Change in y = 3
Change in x = 1
3 / 1 = 3
So, the rate of change is 3.