16x² - 81 This equation is in difference of square form. we know that if it is difference of square then our answer should look like ( x+y) ( x-y) According To Question 16x² - 81 (4x - 9) { because 4 *4 = 16 and 9 * 9 = 81 } (4x - 9) ( 4x + 9) is our answer