Li Ming was born in July, and 13 is added to twice his age this year, exactly the number of days in July. How old is Li Ming?
李明是7月份出生的，他今年年龄的2倍加上13，正好是7月的天数．李明今年多少岁？
<gadget id="calculator">31 - 13</gadget>
<output>18</output>

<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<result>9</result>