The data is linear as the x and y are both increasing at a set amount. X increases by 2 each time Y increases by 4. Our slope would be 2x because every time x goes up 1 y goes up 2. With that knowledge I can figure that if you increased the point -1,17 by the slope to get 0,21 that would be the y intercept. Thus the equation should be y=2x+21
you divide 250 by 15 to get the amount of rotations per month, then once you get that answer which is 16.6666667, you then multiply that number by 9 and there is your answer
