I need help with this simple interest question

An automotive dealer borrowed $9900.00 from the Bank of Montreal on a demand note on May 9. Interest on the loan, calculated on the daily balance, is charged to the dealer's current account on the 9th of each month. The automotive dealer made a payment of $2400 on July 14, a payment of $4000 on October 1, and repaid the balance on December 1. The rate of interest on the loan on May 9 was 6% per annum. The rate was changed to 6.3% on August 1 and to 6.55% on October 1. What was the tota interest cost for the loan? The total interest cost for the loan is $ -] (Round the final answer to the nearest cent as needed. Round all intermediate values to six decimal places as needed.)