Dad is 40 years old this year, and Mingming is 10 years old this year. How many times later, Dad's age will be three times that of Mingming.
爸爸今年40岁，明明今年10岁，再过多少，爸爸岁数是明明的3倍．
<gadget id="calculator">40 - 10</gadget>
<output>30</output>

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

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

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

<result>5</result>