Myerson borrowed $8,500 at 9% ordinary interest for 200 days. after 120 days, he made a partial payment of $4,000. what is the final amount due on the loan?

Interest due at the end of 120 days
= 8500(120/365)(.09) = 251.51

so of his $4000 payment, $3748.49 will go towards reducing the debt.
so balance owing = 8500 - 3748.49
= 4751.51

interest for the remaining 80 days
= 4751.51(.09)(80/365) =93.73

total owing at the end = 4751.51+93.73
= $4845.23