C++ Sequential file Calculator

See attached. I already completed the sequential file (mortgage_14.cpp) and the addtional files attached. I lost my way somehow.

the assignment:

Further modify your program so it allows the user to select which way they want to calculate a mortgage.
1- by input of the amount of the mortgage, the term of the mortgage, and the interest rate of the mortgage payment

OR

2- by input of the amount of a mortgage and then select from a menu of mortgage loans:

7 year at 5.35% 15 year at 5.5% 30 year at 5.75%

Use an array for the mortgage information and read the interest rates and other information into an array read from a sequential file. In either case, display the mortgage payment amount. Then, list the loan balance and interest paid for each payment over the term of the loan. On longer term loans, the list will scroll off the screen. Do not allow the list to scroll off the screen, but rather display a partial list and then allow the user to continue the list. Allow the user to loop back and enter a new amount and make a new selection, or quit. Insert comments in the program to document the program.
The user should be told what the invalid entry was and why it was invalid if they enter a zero or negative amount. They should then be prompted again to reenter a valid amount.
The program should use at least three distinct classes including an abstract base class with at least one virtual method. A concrete class must inherit from this base class and implement any abstract methods in the base class. Each method should have a limited scope and your classes should implement several methods, each of which implements a small part of the task. Do not lump all the functionality into a single class. While the exact format of your classes and structure is up to you, I expect your code to look good and be easy to read and understand.
Post to the source for your program (all files needed to build the program without any temporary files or the final .exe)