Xiaoli's mother deposited 6,000 yuan in the bank for three years. The interest tax rate at that time was 20%. When it was due, she took out the principal and after-tax interest totaling 6,570.24 yuan. What is the annual interest rate for the three-year period?
小丽的妈妈把6000元钱存入银行，定期三年，当时的利息税率为20%，到期时取出了本金和税后利息共6570.24元，三年定期的年利率是多少？
<gadget id="calculator">6_570.24 - 6_000</gadget>
<output>570.24</output>

<gadget id="calculator">6_000 * 3</gadget>
<output>18_000</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">6_000 * 3 * (1/5)</gadget>
<output>3_600</output>

<gadget id="calculator">18_000 - 3_600</gadget>
<output>14_400</output>

<gadget id="calculator">570.24 / 14_400</gadget>
<output>0.0396</output>

<result>0.0396</result>