Answer: 9b - 8b
Step-by-step explanation:
ou need two factors that you will multiply together to give you -72b^2 and at the same time when you add this two factors it will give you + b . Check; 9b X -8b = -72b^2 and 9b + (-8b) = b , that is why 9b and -8b are the factors and they will replace the middle value
