You and Your Roommates Want to Subscribe to a Movie

You and your roommates want to subscribe to a movie rental service. You have two choices: Movies-R-Us charges $15/month, plus $3.50 per movie rented, and See-It-Now charges $7.95/month, plus $5 per movie rented.
A) For each choice, write an equation giving the cost c for renting n movies a month.
B) Which choice should you make, under different scenarios? (For example, you watch lots of movies, you watch only occasionally, etc.) Give your reasoning, perhaps supporting your idea with a graph.