A supermarket has an average of 60 people queuing up to pay per hour, and each cashier can handle 80 people per hour. In a certain period of time on a certain day, the supermarket has only one cashier working, and no customers line up within 4 hours after the payment starts. If there were two cashiers working at that time, no one would line up no matter how many hours the payment started.
某超市平均每小时有60人排队付款，每一个收银台每小时能应付80人，某天某时段内，该超市只有一个收银台工作，付款开始4小时就没有顾客排队了．如果当时有两个收银台工作，哪么付款开始多少小时就没有人排队了．
<gadget id="calculator">80 * 4</gadget>
<output>320</output>

<gadget id="calculator">4 * 60</gadget>
<output>240</output>

<gadget id="calculator">320 - 240</gadget>
<output>80</output>

<gadget id="calculator">80 * 2</gadget>
<output>160</output>

<gadget id="calculator">160 - 60</gadget>
<output>100</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>