Answer pls

How can you tell when x and y are not directly proportional?

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

Will give brainliestbased on the topographic map of mt. st. helens, what is the contour interval if the volcano height is 2,950 m?