Calculate the Rate of change

The rate of change is -5. this can be calculated by taking two points, let’s do (0,30) and (3,15). subtract one coordinate from the other (doesn’t matter which one is which) using the formula (y2-y1)/(x2-x1) = rate of change. so that looks like this: (15-30)/(3-0)= -15/3= -5, therefore the rate of change is -5.

21, i'm pretty sure it's right lol