A Simple Interest Question.

I apologise for the long question, but I need help "interpreting". I am looking for help concerning 1b.

*1. Kevin wants to purchase household appliances worth $1800, $2400, and $900. Each appliance us offered to Kevin for 12 months interest free. He is charged a $25 application fee for each appliance as well as account-keeping fees of $2 per month for each of the three accounts.*

*a. If all three appliances are paid off within 12 months how much will Kevin have paid in total? (*The answer here is $5247).

*b. Kevin doesn't think he can pay off all three appliances in 12 months. If Kevins still owes $2000 in total at the end of the 12 months, what will this amount increase to if the interest rate is charged on the previous 12 months?*

Am I supposed to calculate the interest for the $2000 owing or the $5247 from 1a?