I need help with the business math problem question:

"Ninety days ago Stella signed an agreement with Manon requiring her to make three payments of $400 plus interest 90, 150, and 210 days, respectively, from the date of the ageement. Each payment was to include interest on the $400 principal at the rate of 13.5% from the date of the ageement. Stella now wants Manon to renegotiate the agreement and accept a single payment 30 days from now, insted of the three scheduled payments. What payment should Manon require in the new agreement if money is worth 8.5%?"

Thank you in advance for your help!