Rebecca made a mosaic wall using 42 black tiles, 35 blue, and 23 red tiles. What percent of the mosaic wall uses red tiles?

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.