Problem 9 A real estate agent is considering changing her cell phone plan. There are three plans to choose from, all of which involve a monthly service charge of $20. Plan A has a cost of $.45 a minute for daytime calls and $.20 a minute for evening calls. Plan B has a charge of $.55 a minute for daytime calls and $.15 a minute for evening calls. Plan C has a flat rate of $80 with 200 minutes of calls allowed per month and a charge of $.40 per minute beyond that, day or evening. a a. Determine the total charge under each plan for this case: 120 minutes of day calls and 40 minutes of evening calls in a month. b. Prepare a graph that shows total monthly cost for each plan versus daytime call minutes