The younger brother is (a+5) years old this year, the older brother is 3a years old this year, the older brother is 30 years old this year, how old is the younger brother this year?
弟弟今年的年龄是(a+5)岁，哥哥今年的年龄是3a岁，哥哥今年30岁，弟弟今年多少岁？
<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<result>15</result>