9y + 3(y + 6) = 15y + 21 Reorder the terms: 9y + 3(6 + y) = 15y + 21 9y + (6 * 3 + y * 3) = 15y + 21 9y + (18 + 3y) = 15y + 21 Reorder the terms: 18 + 9y + 3y = 15y + 21 Combine like terms: 9y + 3y = 12y 18 + 12y = 15y + 21 Reorder the terms: 18 + 12y = 21 + 15y Solving 18 + 12y = 21 + 15y