Tom and Marie have a 30-year $150,000 mortgage with an 8% interest rate convertible monthly. Immediately after the 120th payment, they refinance the mortgage. The interest rate is reduced to 6.5%, convertible monthly, and the term is reduced to 20 years (so there are 10 years of payments remaining). They also make an additional payment of $20,000 at the time of refinancing. Calculate their new monthly payment.

The answer is 1267.0484, but I'm not sure how to get there.