At 8 o'clock one morning, there were already 630 passengers waiting for the ticket check at the entrance of Wuchang Railway Station. At this time, there are still a number of people (the same number per minute) coming to the station to prepare for entering the station every minute. In this way, if 5 ticket gates are set up, passengers can be discharged in 18 minutes. If 9 ticket gates are set up, passengers can be discharged in 8 minutes. Now it is required to complete passengers in 3 minutes. How many ticket gates need to be set up?
某天早晨8点，武昌火车站进站处已有630名旅客等候检票进站．此时，每分钟还有若干人(每分钟同样多)前来进站处准备进站．这样，如果设立5个检票口，18分钟可以放完旅客，如果设立9个检票口，8分钟可以放完旅客，现在要求3分钟放完旅客，则需要设立多少个检票口？
<gadget id="calculator">18 * 5</gadget>
<output>90</output>

<gadget id="calculator">8 * 9</gadget>
<output>72</output>

<gadget id="calculator">90 - 72</gadget>
<output>18</output>

<gadget id="calculator">18 - 8</gadget>
<output>10</output>

<gadget id="calculator">18 / 10</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">(9/5) * 18</gadget>
<output>162/5 = around 32.4</output>

<gadget id="calculator">90 - (162/5)</gadget>
<output>288/5 = around 57.6</output>

<gadget id="calculator">3 * (9/5)</gadget>
<output>27/5 = around 5.4</output>

<gadget id="calculator">(288/5) + (27/5)</gadget>
<output>63</output>

<gadget id="calculator">63 / 3</gadget>
<output>21</output>

<result>21</result>