To simplify the expression (5x^2 - 21x - 20) / (5x^2 - 16x - 16), we can check if there are terms that are needed to be added or subtracted. In this case, there are none. We just check the factors of each polynomial above and below. The factored equation of the numerator is (x-5)*(x + 4/5) while that below is (x-4)* (x + 4/5). In this case, we cancel (x + 4/5). Hence the answer is (x-5) / (x-4)