The father is 50 years old this year, and the son is 24 years old this year. How many years ago, the age of the father was three times that of the son.
父亲今年50岁，儿子今年24岁，多少年前父亲的岁数是儿子的3倍．
<gadget id="calculator">50 - 24</gadget>
<output>26</output>

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

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

<gadget id="calculator">24 - 13</gadget>
<output>11</output>

<result>11</result>