Li Ming is 21 years old this year, and Xiaoyong is 5 years old. After many years, Li Ming's age is three times that of Xiaoyong.
今年李明21岁，小勇5岁，多少年后，李明的年龄是小勇的3倍．
<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">21 - 15</gadget>
<output>6</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<result>3</result>