Simplify: 7ax3+5x2a-9a÷3

Precalculus question, image attached.

Clarence wants to buy a new car. he finds an ad for a car that costs 27,200 dollars. suppose his local sales tax is 7%. -how much would he have to pay? -what is the cost of the car including tax? -if clarence has 29,864 saved, can he pay cash to buy the car?

Which will form a composite function?