How do i solve a quadratic inequality?

The amount of energy it takes to lift a box might be a function of which of the following

School has 204 sixth grade students. if the sixth grade is 30% of the total school, how many students are in the middle school?

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