You borrowed $27,000 for 5 years. You promised to pay back the principal and the interest in one lump sum. After 5 years, you paid the lump sum of $54,000. What was the annual rate in percent? Here the interest is assumed to be calculated by the rule of simple interest, that is, if you borrow $A for n years with the interest rate r, your total interest will be $nrA, the product of n, r and A.

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