The father is 47 years old this year, and the son is 19 years old this year. How many years ago, the father was 5 times the age of the son.
父亲今年47岁，儿子今年19岁，多少年前父亲的年龄是儿子的5倍．
<gadget id="calculator">47 - 19</gadget>
<output>28</output>

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

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

<gadget id="calculator">19 - 7</gadget>
<output>12</output>

<result>12</result>