A linear function must have x and y with powers of 1. Also it can't something like x^2 - y^2 = 5
x^2 - y^2 = 0 is the only exception I can think of, but that really is a system of equations. If you graph it. you get two equations which cross at 0 and nowhere else.
–5 × 0.75 × 20 could be rewritten (applying the associative property) as –5 × (0.75 × 20). I chose this configuration because 0.75 * 20 is 15. Next, evaluate -5(15). This is -75. This matches Answer D.