Exercise 58 Page 57

We will first think of the quantity inside the parentheses as a whole. To solve this equation using mental math we want to think about what it means in words. 9 = 4+ (- y) 9 equals 4 plus another number. We know that if we add 5 to 4 we get 9. This means that what is inside the parentheses equals 5. - y=5 Therefore, y=-5.