A mobile phone service provider has three different data plans for its customers:

Package A: For $39.99 per month, 4 gigabytes are provided. Additional data costs $10 per gigabyte.

Package B: For $59.99 per month, 8 gigabytes are provided. Additional data costs $5 per gigabyte.

Package C: For $69.99 per month, unlimited data is provided.

Write a program using C++ that calculates a customer's monthly bill. It should ask which package the customer has purchased and how many gigabytes were used. It should then display the total amount due.