What A levels teachers need to do to get a degree

The approach that contends psychology must study internal mental events in order to fully understand behavior is:

Lydia finds a car that costs 13,000, and she has 2,500 saved for a down payment. if she qualifies for a 5% interest rate, how much will the interest be calculated on? 13,000? 12,000? 15,500? 10,500? in : )

How do you do this? i’ve marked the correct answer but i can’t seem to calculate