Business When a loan is paid off early, a portion of the finance charge must be returned t...

Business When a loan is paid off early, a portion of the finance charge must be returned to the borrower. By one method of calculating the finance charge (called the rule of 78), the amount of unearned interest (finance charge to be returned) is given by

where u represents unearned interest, f is the original finance charge, n is the number of payments remaining when the loan is paid off, and q is the original number of payments. Find the amount of the unearned interest in each of the given cases.

Original finance charge = $800, loan scheduled to run 36 months, paid off with 18 payments remaining