A store has been selling a popular game at the price of p = $40 per unit, and at this price players have been buying x = 60 units per month. When the price is set at p = $45 per unit, players buy x = 50 units per month.

A: Assuming this relationship is linear, find an equation of the form p = mx + b that relates the price p to the number of units sold.

B: Find an equation that represents the total revenue if x units are sold

C: The store buys the games for $30 per unit sold, and also has fixed costs of $500 per month. Find an equation of the form C = mx + b that represents the total cost to the store for selling x units of the game.

D: Find and simplify an equation that represents the monthly profit for this store.

2: A bookstore has determined that if it sets the price of a popular book at x dollars per copy, then its monthly profit can be represented by the equation p = (500 - 20x)(x-3), which is graphed below.