Microbiotics currently sells all of its frozen dinners cash-on-delivery but believes it can increase sales by offering supermarkets 1 month of free credit. The price per carton is $70, and the cost per carton is $50. The unit sales will increase from 1,170 cartons to 1,230 per month if credit is granted. Assume all customers pay their bills and take full advantage of any credit period offered. If the interest rate is 1% per month, what will be the change in the firm's total monthly profits on a present value basis if credit is offered to all customers? Note: Do not round intermediate calculations. Round your answer to 2 decimal places. If the interest rate is 1.5%