This year, the younger brother is 6 years old and the older brother is 15 years old. When the sum of their ages is 65, how old is the younger brother?
今年弟弟6岁，哥哥15岁，当两人的年龄和为65时，弟弟多少岁．
<gadget id="calculator">15 - 6</gadget>
<output>9</output>

<gadget id="calculator">65 - 9</gadget>
<output>56</output>

<gadget id="calculator">56 / 2</gadget>
<output>28</output>

<result>28</result>