A loan at $\displaystyle {j_1} = 9\% $ is being repaid by monthly payments of $750 each. The total principal repaid in the 12 monthly installments of the 8th year is $400. What is the total interest paid in the 12 installments of the 10th year?

The answer is of course $8,524.76

The answer makes use of the fact that the entries in the principal repaid column (especially in a no rounding scenario) are in the ratio of 1 +i.

An interesting question of course is whether it's possible to solve for the amount of the loan and loan term from the given information.

Apparently, it is.