The correct answer is: "18 percent"
The interest rate is the amount charged for the use of a financial asset (for example, money during a certain period of time = a loan), it is paid by the borrower, earned by the lender and it is usually expressed as a percentage that is applied to the total value of the asset, called principal.
Banks will make the most money in those operations in which they act as lenders and a higher percentage is applied to the principal. In general, banks demand a higher return (a higher interst) to participate in operations that involve a higher risk, for example, lending money to a country with serious public deficit problems.