Xiao Ming is 7 years old this year, and his mother is 37 years old this year. How many years later, his mother's age will be exactly three times that of Xiao Ming.
小明今年7岁，妈妈今年37岁，再过多少年妈妈的年龄正好是小明的3倍．
<gadget id="calculator">37 - 7</gadget>
<output>30</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 7</gadget>
<output>8</output>

<result>8</result>