Please help I am stuck :/

Using the side-splitter theorem, daniel wrote a proportion for the segment formed by luke segment de. what is ec?

With finding limits of multi variable !

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.