Please what is the answer

Itook a better photo of the question so y’all can see it i hope it’s a fine photo

Use set builder notation to represent the following set: { -3, -2, -1, 0}

Suppose you are an avid reader and are looking to save money on the cost of books instead of paying about $20 for each book, you decide to look into purchasing a kindle for $120 you can purchase e-books for about $5 each 1. find the slope-intercept equation for the cost of the hard copy of books using x to represent the number of books 2. find the slope-intercept equation for the cost of the kindle with cost of e-books using x to represent the number of books