The number y, in millions, of drug prescriptions filled by mail order in the united states from 1995 through 2008 can be modeled by y = 13.0t + 20 for 5 ≤ t ≤18 where t is the year with t = 5 corresponding to 1995.

a) according to the model, when did the number of prescriptions filled by mail order reach 100 million?

b) what is the slope of the model and what does it tell you about the number of prescriptions filled by mail in the united states?

c) do you think the model can be used to predict the number of prescriptions filled by mail order in the united states beyond 2008? if so, for what time period?

d) explain, both algebraically and graphically, how you could find the number of prescriptions filled by mail order reaches 300 million.