Financial Functions

I am not a true financial type. What I need is a formula that will tell a person how much money they will pay, over time, in a revolving credit account.

Example:
Mary has $600.00 on her Credit Card. She makes a minumum payment (4% of balance or $15,00, whichever is greater) each month. How long will it take her to pay in full, and what is the cumulative value of her payments.

In building a simple amortization table based on the above, I know it will take 51 payments to pay off the credit card and the sum of all payments amounts to $843.41.

But I know there has to be a way to do this without having a table that will cover all the variables that might come up with Mary's (or anyone else's) credit card. They change the interest rate, or minimum payment, etc.

In the attached zip file:

Cell D3 has the beginning balance
Cell D4 has the interest rate

Cells G3 & G5 have the paramaters for minimum payment.

Cell D6 has the time it will take to pay off.

Cell G6 has the total of all payments made until paid off.

I would like to know if there are functions that could return the values in Cells D6 & G6 without the need to have the table.

My reason is that I want to show how a Debt Snowball would work with multiple revolving accounts.