please show your work with each problem. thank you

Problem 5. [20] I run a clothing store. We are having a store wide sale - everything is 20% off. Also, we are offering a promotion where every purchase will get a $10 rebate. Customers may choose to either apply the discount first or get the rebate first. a. [5) Let r be the price of an item. Find an equation f() that gives the price of an item after the 20% discour count. b. [5] Let r be the price of an item. Find an equation g(r) that gives the price of an item after the $10 rebate. c. [5) What is fog(I) d. [5) What is go f (1)