Answer:
Step-by-step explanation:
(a) Your $160 is correct.
(b) No, this is not a proportional relationship, because the graph does not go through the origin. That, in turn, is because there is a fixed, up-front cost of $120.
(c) The total cost as a function of the number of months, m, is
TC(m) = $120 + ($40/month)m
