This is programming exercise 5a-5c that has not been answered in the textbook solutions for Microsoft Visual C# 2015.

5a. Create an application named AutomobileDemo that prompts a user for data for eight Automobile objects. The Automobile class includes auto-implemented properties for ID number, make, year and price. Override the ToString() method to return all the details for an Automobile. During date entry, reprompt the user if any ID number is a duplicate. Sort the objects in ID number order, and display all their data as well as a total of all their prices.

5b. Using the Automobile class as a base, derive a FinancedAutomobile class that contains all the data of an Automobile, plus fields to hold the amount financed and interest rate. Override the parent class ToString() method to include the child class' additional data. Create a program named AutomobileDemo2 that contains an array of four FinancedAutomobile objects. Prompt the user for all the necessary data, and do not allow duplicate ID numbers and do not allow the amount financed to be greater than the price of the automobile. Sort all the records in ID number order and display them with the total price for all FinancedAutomobiles and the total amount financed.

5c. Write an application named AutomobileDemo3 that uses an extension method for the FinancedAutomobile class. The method computes and returns a FinancedAutomobile's monthly payment due (1/24 of the amount financed). The application should allow the user to enter data for four objects and then display all the data for each.