a) For principal amount P, interest rate r, and number of years t, the amortization formula for the monthly payment A is ...
... A = P(r/12)/(1 -(1 +r/12)^(-12t))
... A = 22500·(0.06/12)/(1 -(1 +0.06/12)^(-12·20)) ≈ 161.20
The monthly payment is $161.20.
b) After 240 payments, the amount repaid is
... $161.20·240 = $38,688
c) (22500/38688)·100% = 58.2% is paid toward principal
The remaining amount, 41.8% is paid toward interest.
