Please Help on Both Parts, I am continually getting Part B wrong and I do not understand why.

The Mendez family is considering a mortgage loan of $348,500 at an annual interest rate of 6.7%.

(a) How much greater is their mortgage payment if the term is 20 years rather than 30 years? $ (b) How much less is the amount of interest paid over the life of the 20-year loan than over the life of the 30-year loan?

Equation is as follows:

348500((0.067-:12)/(1-(1+(0.067)/(12))^(-12*30))) For thirty years

348500((0.067-:12)/(1-(1+(0.067)/(12))^(-12*20))) For twenty years