Help 4,5 and ,6 please

Omar is going on a road trip! the car rental company offers him two types of cars. each car has a fixed price, but he also needs to consider the cost of fuel. the first car costs $90 to rent, and because of its fuel consumption rate, there's an additional cost of s0.50 per kilometer driven.

Find the difference (8ab+a+2) - (3ab+6)

Find the solution of each of the following.