This is a simple interest problem. We are going to use the formula: Where I is the interest she has to pay for her loan, P is the amount she financed, r is the interest rate (in decimal), and t is the number of years.
Replace the values to get:
Now that we have the interest she paid, we just need to add them to the value she paid to get the total cost she paid:
We can conclude that the total cost of the car that she financed will be $21,077.46
Answer: Once your 0% introductory APR period is over, you'll be charged a new interest rate and may even owe interest on any unpaid balance from before.