If y is directly proportional to x and if y = 20 when x = 6, what is the value of y when x = 9 ?
(a) 10/3
(b) 40/3
(c) 23
(d) 27
(e) 30
can someone explain this one for me?

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