3. A salesperson makes a base salary of $2100 per month. Once he reaches $42000 in total sales, he earns an additional 5% comission on the amount of sales over $42000. a. (2 points) Write a piecewise-defined function to model the salesperson's total monthly salary Sx) (in dollars) as a function of the amount of sales x. b. (2 points) Graph the function. Indicate the numerical scale on the horizontal and vertical axes of your graph, and indicate which axis represents the salary and which is the sales. c. (1 point) If the salesperson had $80000 in sales, how much was his salary for that month? d. (2 points) If the salesperson's total salary for a month was $4500, how much were his total sales for that month