Gamers: Two dollars for every game downloaded. Game World: $15 per month and $0.50 per game downloaded.
a) How much money would it cost if you downloaded 6 games from Gamers? Show your work, using the equation c=2d, where c is the cost and d is the number of downloads.
b) Write an equation for the cost per month at Game World, using c for cost and d for downloads.
c) Which equation is represented in the graph below, Gamers or Game World? Justify your answer using mathematical reasoning.