9. Greg needs at least $1.60 in stamps to mail a package. He has 28¢ and 4¢ stamps. He can use no more than twenty 4¢ stamps as he only has one book left. a) Write a system of linear inequalities to represent this situation, then graph.
b) Using your graph, give two possible combinations of stamps that Greg can use to ensure he mails his package with the correct postage.