Lingling is 10 years old this year. The teacher said to Lingling: "Three years ago, my age was three times your age at that time." How old is the teacher this year?
玲玲今年10岁，老师对玲玲说："三年前我的年龄是你那时年龄的3倍．"老师今年多少岁？
<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">30 - 9</gadget>
<output>21</output>

<gadget id="calculator">3 + 21</gadget>
<output>24</output>

<result>24</result>