The annual interest rate earned by an investment increased by 6 percent from last year to this year. If the annual interest rate earned by the investment this year was 15.90 percent, what was the annual interest rate last year?  Select the correct option:
A) 20%
B) 18%
C) 16%
D) 25%
E) 15%
let i = interest rate   i(this year) = i(last year) + 0.06i(last year) = 1.06i(last year)   15.90 = 1.06 x i(last year)   i(last year) = 15.90/1.06 = 1590/106= 
<gadget id="calculator">1590/106</gadget>
<output>15</output>
15%   Answer : 15%
<result>E</result>
The annual interest rate earned by an investment increased by 6 percent from last year to this year. If the annual interest rate earned by the investment this year was 15.90 percent, what was the annual interest rate last year?