The number of students in Mr. Boggs’s homeroom is equal to b. Add the total number of students in each class and set it equal to 90.
90 = b + 1.5(b + 2) + 15 + (2b – 9)
Use the Distributive Property, and collect like terms. 90 = b + 1.5b + 3 + 15 + 2b – 9
90 = 4.5b + 9