Xiao Ming is 12 years old this year, and his father is 40 years old. When Xiao Ming was so old, his father was 5 times as old as Xiao Ming.
小明今年12岁，爸爸40岁．在小明多少岁的时候，爸爸的年龄是小明的5倍．
<gadget id="calculator">40 - 12</gadget>
<output>28</output>

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">28 / 4</gadget>
<output>7</output>

<result>7</result>