A machine salesperson earns a base salary of $ 20,000 plus a commission of $ 200 for every machine he sells.

a. Write an equation that shows the total amount of income the salesperson earns - m(x)-, if he sells x machines in a year.
 

b. How many machines does he need to sell in order to make $ 90,000?


c. If you were to graph the equation you wrote for part a\displaystyle {a}, what would the y-intercept represent?