Xiao Ming is 7 years old this year, and his father is 33 years old this year. When Xiao Ming was old, his father was three times his age.
小明今年7岁，爸爸今年33岁，小明多少岁时，爸爸年龄是他的3倍．
<gadget id="calculator">33 - 7</gadget>
<output>26</output>

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

<gadget id="calculator">26 / 2</gadget>
<output>13</output>

<result>13</result>