Loan for 1500 dollars at 3% interest for 18 months how much will you pay back

Nowt, because there's no legal loan agreement.
Although if you can show me the working we'll see what happens..

Dutchess - the answer will depend on how many payment periods there are. If the loan is paid in equal monthly installments there will be 18 payments, and the interest charged for each period is 3%/18.