A woman owns 21 pets. Each of her pets is either a cat or a bird. If the pets have a total of 76 legs, how many cats and how many birds does the woman own?

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.