What is the monthly payment for a $20,230 loan at 11.5 percent for 20 years?

The main formula is 
M= P (i(1+i)^n) / (1+i)^n) - 1
M: monthly payment
P: mortgage principale=  $20,230
i=montly interest, 11.5%=11.5/100=0.115, i= 0.115/12=0.009
n=number of months=12x20(years)=240 months

M= $20,230(0.009(1.009)^240) / (1.009)^240-1=$20,230 x 0.0077 / 8.58-1
M=$20.57

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