If a = -9 and b = -4, what is the value of ab?

Given the following statements, which is the best

The two square pyramids are similar. find the total volume of both pyramids if the ratio of their surface areas is 9/16

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