22a) Matts' weekly fee is $7.50. We know this is by looking at the Y-axis. If he doesn't sell any books at the beginning of the week, his earnings are at -$7.50. We can assume that he pays that much for internet fee.
22b) Matt makes $1.50 for each book he sells. We know this because if you look at (5,0) and then the next one (6, 1.5), we see that his Y-value has increased by $1.50, which is equal to one book because 6 - 5 = 1 book.
22c) y = 1.5x - 7.5
22d) I'm going to assume that question means $30 in profit. Let's plug in the 30 in the equation. 30 = 1.5x - 7.5. Simplify. Matt has to sell 25 books to make $30
