The problem adds a twist to the compound interest calculation by having the bank account owner depositing a fixed amount of money annually. The interest rate is compounded annually.
This function allows the user to input four variable inputs: the principle amount in the account (principle_amount), the yearly addition/deposition (yearly_deposition), the number of years elapsed (number_years), and the yearly interest rate (interest_rate) in decimals eg. 0.05 for a 5% interest rate.
It outputs the total amount y (in the bank account) after the number of years elapsed.