I need help what’s the answer to this Y = x + 1

2.5 milligrams is equivalent to how many grams

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

The cost of using a service is $0.25 per min. what equation correctly represents the total cost c, in dollars, for d days of use?