The father is 45 years old this year, and the son is 15 years old this year. How many years ago, the age of the father was 11 times the age of the son.
父亲今年45岁，儿子今年15岁，多少年前父亲的年龄是儿子年龄的11倍．
<gadget id="calculator">45 - 15</gadget>
<output>30</output>

<gadget id="calculator">11 - 1</gadget>
<output>10</output>

<gadget id="calculator">30 / 10</gadget>
<output>3</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<result>12</result>