My sister is 22 years old this year, and my younger sister is 15 years old this year. How many years ago my elder sister was twice as old as my younger sister.
姐姐今年22岁，妹妹今年15岁．多少年前姐姐的年龄是妹妹的2倍．
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">30 - 22</gadget>
<output>8</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">8 / 1</gadget>
<output>8</output>

<result>8</result>