A mobile phone service has three different data plans for its customers: PLAN A: For $19.99 per month, 2 gigabytes are provided. Additional usage costs $8.00 per gigabyte. PLAN B: For $59.99 per...

Write a program that calculates a customer’s monthly bill. It should input the customer name, which plan was purchased, and how many  gigabytes were used. It should then create a bill that includes the input information and the total amount due. It should also display how much money plan A customers would save if they purchased plan B or C, and how much money plan B customers would save if they purchased plan C. If there would be no savings, no message should be printed. Wherever possible, use named constants instead of numbers.