I believe this problem is unsolvable by ordinary means.
John loaned $72,000 from the bank to be paid over 10 years.
The bank charges compound interest,
Calculate the annual interest rate if his monthly installments was $890.
This is an Amortization problem.
We are given: .
We want the annual interest rate,
. . The periodic interest rate is: .
Now all you have to do is solve for . . . then multiply by 12.
I'll wait in the car . . .