Given P(A)=0.78P(A)=0.78, P(B)=0.65P(B)=0.65 and P(A\cup B)=0.873P(A∪B)=0.873, find the value of P(A\cap B)P(A∩B), rounding to the nearest thousandth, if necessary

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