Could you explain interest expense?

Mike's Motors Corp. manufactures motors for dirt bikes. The company requires a minimum $30,000 cash balance at each month-end. If necessary, the company borrows to meet this requirement, at a cost of 3% interest per month (paid at the end of each month). Any cash balance above $30,000 at month-end is used to repay loans. The cash balance on July 1 is $43,000, and the company has no outstanding loans at that time. Forecasted cash receipts and forecasted cash payments (other than for loan activity) are as follows. July August September Cash Receipts $ 94,000 120,000 159,000 Cash Payments $122,000 108,900 136,400 Prepare a cash budget for July, August, and September. (Negative balances and Loan repayment amounts (if any) should be indicated with minus sign. Round your final answers to the nearest whole dollar.) MIKE'S MOTORS CORP. Cash Budget For July, August, and September July August September Beginning cash balance $ 43,000 $ 30,000 $ 30,000 Cash receipts 94,000 120,000 159,000 Total cash available 137,000 150,000 189,000 Cash payments 122,000 108,900 136,400 Interest expense Preliminary cash balance 15,000 41,100 52,600 Additional loan (loan repayment) 15,000 (11,100) (3,900) Ending cash balance $ 30,000 $ 30,000 $ 48,700 Loan balance Loan balance, Beg. of Month $ 0 $ 15,000 $ 3,900 Additional loan (loan repayment) 15,000 (11,100) (3,900) oan balance, Month-end $ 15,000 $ 3,900 $ 0