The uncle is 20 years older than Xiao Ming, and next year the uncle will be three times Xiao Ming's age. How old is Xiao Ming?
叔叔比小明大20岁，明年叔叔的年龄是小明的3倍．小明今年多少岁．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

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

<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<result>9</result>