At a certain ticket office, there were already people queuing up before the tickets were sold. By the time the tickets were sold, there were already 75 people in line. There is no longer a queue. If two windows are opened, no one will line up after 5 minutes, and if three windows are opened, no one will line up after a few minutes?
某个售票处，在卖票之前，就已经有人排队，到开始卖票时，已经排了75人，卖票后，由于每分钟来买票的人数一样多，因此，一个窗口花15分钟才不再有人排队．如果开两个窗口，则经过5分钟不再有人排队，如果开三个窗口，则经过几分钟不再有人排队？
<gadget id="calculator">2 * 5</gadget>
<output>10</output>

<gadget id="calculator">1 * 15</gadget>
<output>15</output>

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

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

<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 5</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">10 - (5/2)</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">3 - (1/2)</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(15/2) / (5/2)</gadget>
<output>3</output>

<result>3</result>