Abbey purchased a house using a fixed rate mortgage. the annual interest rate is 4.2% compounded monthly for 20 years. the mortgage amount is $235,000. what is the monthly payment on the mortgage

Converting 4.2% annual rate = 4.2/1,200 = .0035 monthly rate
(1.0035)^12 = 4.2818% compounded monthly.
4.2818 / 1,200 = 0.0035681667

Monthly Payment = ( 0.0035681667 + [ 0.0035681667 / [(1.0035681667)^240 -1] )] * 235,000

Monthly Payment = ( 0.0035681667 + [ 0.0035681667 / 1.3509883519]) * 235,000

Monthly Payment = ( 0.0035681667 + 0.0026411528) * 235,000

Monthly Payment = 0.0062093195 * 235,000

Monthly Payment = $1,459.19

See, it's just that easy!!! LOL

Source:
http://www.1728.org/loanform.htm
(a worked out example of the formula)