= A real estate agent is considering changing her land line 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 $.38 a minute for daytime calls and $.17 a minute for evening calls. Plan B has a charge of $.47 a minute for daytime calls and $.14 a minute for evening calls. Plan C has a flat rate of $75 with 275 minutes of calls allowed per month and a charge of $.36 per minute beyond that, day or evening. 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. (Do not round intermediate calculations. Round your answer to 2 decimal places.) Cost for Plan A Cost for Plan B Cost for Plan C b. If the agent will only use the service for daytime calls, over what range of call minutes will each plan be optimal? (Round each answer to the nearest whole number. Include the indifference point itself in each answer.) Plan A is optimal from zero to minutes. Plan C is optimal from minutes onward.