I think it's A. Sorry if I get it wrong.
Population. Population is the amount of whatever is inisde
a. The independent variable is r. The dependent variable is m.
b. The domain is the set of numbers used in the independent variable. You can rent 0 videos, or 1 video, or 2 videos, etc., up to the amount of money you have. If you rent 0 videos, you are left with m = 30 - 3r = 30 - 3(0) = 30 - 0 = 30 dollars. If you rent 10 videos, you will have m = 30 - 3(10) = 30 - 30 = 0 dollars left. The domain is {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}. The range is {0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30}. Both the domain and range are discrete.
c. I can't do it online.