My mother is 42 years old this year, and I am 9 years old this year. In (how many) years, my mother will be exactly 4 times my age.
妈妈今年42岁，我今年9岁，再过(多少)年，妈妈的年龄正好是我的4倍．
<gadget id="calculator">42 - 9</gadget>
<output>33</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">33 / 3</gadget>
<output>11</output>

<gadget id="calculator">11 - 9</gadget>
<output>2</output>

<result>2</result>