Exponential growth refers to an increase based on a constant multiplicative rate of change over equal increments of time,that is a percent increase of the original amount over time.
We know she made a down payment of 2500 dollars and she agreed to pay the balance in 24 monthly installments of 350 dollars. Thus we can do simple multiplying of 24 x 350 which gives us 8400. We also need to add in her down payment which is 2500 so in total we got 10900