You are interested in getting data for your cellphone, so you can finally access the internet without using Wi-Fi. You look into a few cell phone companies. Here are two choices you have narrowed down to:

T-Mobile: $55/month for the first 5GB of usage, then its $15 per GB use after (this overage rate will take into account partial usage for each GB, meaning if I go exactly 1/2GB over, I will pay $7.50 [1/2 of the $15]).

American Telephone and Telegraph (ATT): $70/month for the first 8GB of usage, then $10 per GB afterwards (this overage rate does not take into account partial usage. Therefore if you go over by 0.01 GB, you will pay an extra $10).

a. Give a piecewise function for each data plan, where P(d) represents cost for Phoenix Mobile as a function of data d, and R(d) represents cost for RCTT as a function of data d. Only give the function for the first 10GB of data.

b. Sketch both functions on the graph to the right, labeling your axes with the independent and dependent variables.

c. You check your cellphone and see that you use 9.25GB last month. How much would it cost for each data plan?