Xiao Ming does 9 cross-point math problems every minute, and Xiao Gang does three times as much as Xiao Ming every minute. How many more oral arithmetic questions does Xiaogang do than Xiaoming per minute?
小明每分钟做9道口算题，小刚每分钟做的是小明的3倍．小刚每分钟比小明多做几道口算题？
<gadget id="calculator">9 * 3</gadget>
<output>27</output>

<gadget id="calculator">27 - 9</gadget>
<output>18</output>

<result>18</result>