In 2007, the age of the father was 5 times that of the son, and in 2015 the age of the father became 3 times the age of the son. When was the son born?
2007年父亲的年龄是儿子的5倍，到2015父亲的年龄变成儿子年龄的3倍，儿子是在多少年出生的．
<gadget id="calculator">2_015 - 2_007</gadget>
<output>8</output>

<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<gadget id="calculator">24 - 8</gadget>
<output>16</output>

<gadget id="calculator">5 - 3</gadget>
<output>2</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">2_007 - 8</gadget>
<output>1_999</output>

<result>1_999</result>