The father is 30 years older than the son, and the mother is 25 years older than the son. The sum of the ages of the father and mother is 75 years. What is the age of the son?
父亲比儿子大30岁，母亲比儿子大25岁，父亲与母亲的年龄之和是75岁，求儿子的年龄是多少岁．
<gadget id="calculator">30 - 25</gadget>
<output>5</output>

<gadget id="calculator">75 - 5</gadget>
<output>70</output>

<gadget id="calculator">70 / 2</gadget>
<output>35</output>

<gadget id="calculator">35 - 25</gadget>
<output>10</output>

<result>10</result>