Four years ago, my elder brother was twice as old as my younger brother. My elder brother is 16 years old this year. How old is my younger brother?
4年前哥哥的年龄是弟弟的2倍，哥哥今年16岁，弟弟今年多少岁？
<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">6 + 4</gadget>
<output>10</output>

<result>10</result>