Since Cammen earns $500 for every car she sells, if she sells a total of x cars, the will earn a commission of 500x.
Then, adding the commission to the base salary, her salary (y) will be:
a)

b)
In order to earn 60,000, the number of cars she needs to sell is:

So Cammem needs to sell a total of 40 cars in order to earn $60,000.