If​ $680 is worth​ $698.70 after three​ months, what interest rate was​ charged?

Solving our equation: r = (1/3)((698.7/680) - 1) = 0.00916667 r = 0.00916667 Converting r decimal to R a percentage R = 0.00916667 * 100 = 0.9167% per month Calculating the annual rate 0.9167%/month × 12 months/year = 11.0004% per year.