This year, the younger brother is 12 years old and the older brother is 18 years old. When the sum of their ages is 50 years old, how old is the younger brother?
今年弟弟12岁，哥哥18岁，当两人的年龄和是50岁时，弟弟多少岁．
<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">50 - 30</gadget>
<output>20</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">12 + 10</gadget>
<output>22</output>

<result>22</result>