Use the formula for the future value of an ordinary annuity to solve for n when A=$10,000, the monthly payment R=$800, and the annual interest rate= r= 9.0%
FV = P x {[1 + R]^N - 1 / R}
10,000 = 800 x {[1.09/12]^N - 1 / 0.09/12}
12.50 = [1.0075^N - 1/ 0.0075]
0.09375=[1.0075^N - 1]
1.09375 =1.0075^N take the log of both sides
N =Log(1.09375) / Log(1.0075)
N =11.993 ~ 12 months.
