Your formula is incorrect . . .
I'm borrowing $300,000 to buy a townhouse,
and can afford to make mortage payments of $2,000 per month
and can obtain a loan from the bank w/ and APR of 7.2%.
How many years will it take to pay off the debt?
. . where: .
We have: .
. . . .and: . , where = number of years.
The formula becomes: .
Divide by 2000: .
Take logs: .
. . It will take about 32 years, 1 month.