"Write a program that displays the appropriate shipping charge based on the region code entered by the user. To be valid, the region code must contain exactly three characters: a letter (either A or B) followed by two numbers. The shipping charge for region A is $25. The shipping charge for region B is $30. Display an appropriate message if the region code is invalid. Use a sentinel value to end the program. Save and then run the program. Test the program using the following region codes: A11, B34, C7, D2A, A3N, C45, and 74TV."