Natalie is considering the purchase of a cellphone service plan. There are two service plans to choose from. Plan A has a monthly charge of $20 plus $0.45 a minute for day- time calls and unlimited eveningight/weekend calls. Plan B has a flat rate of $50 with 200 daytime minutes of calls allowed per month and a cost of $0.40 per daytime minute beyond that, and unlimited eveningight/weekend calls. a. Determine the total charge under each plan for this case: 120 minutes of daytime calls a month. b. Prepare a graph that shows total monthly cost for each plan vs. daytime call minutes. c. Over what range of daytime call minutes will each plan be optimal