in racket

4. (40 Points) You work at a furniture store, where your weekly salary is $240. You also earn a commission of 3% on the portion of your sales over $4000. Write a function called earnings that consumes the dollar amount of sales you had for the week, and produces your earnings for that week. In order to get credit for this problem, you must define and use at least one helper function (you may choose the name and signature of your helper(s)). Use defined constants where appropriate. Make sure each function you define is documented with a signature and a purpose. Each function should be tested using check-expect