Can someone pls help me with this but show ur work ill give u brainliest

Idon’t understand this.. will someone ? will mark brainliest along with 20 points.

Which of the following is the shape of a cross section of the figure shown below

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