Barbara borrows $3500. She agrees to make monthly interest payments on the loan and will build up a sinking fund with monthly deposits to repay the principal with a single payment 21 months from now. If the interest being charged on the loan is j12 = 8% and the interest being earned on the sinking fund is j12= 5.2%, what is the monthly cost of the debt for Barbara?

I got 182.95 but is wrong. please help