student's home is 4,500 meters away from the school. He rides a bicycle every morning at 7:20 and arrives at the school on time at an average speed of 250 meters per minute. One minute after he set off one day, he found that he didn't bring any stationery, so he went home immediately to get it. From the discovery that the stationery was not brought back to the school again, how fast can I not be late (the time to pick up the stationery is 1 minute)?
一个学生的家离学校有4500米，他每天早上骑自行车7：20出发，以平均每分钟250米的速度，刚好准时到校．有一天他出发1分钟后，发现文具没带，立即回家拿．从发现文具没带返回到重新到校，得多快的速度才能不迟到(拿文具的时间为1分钟)？
<gadget id="calculator">4_500 + 250</gadget>
<output>4_750</output>

<gadget id="calculator">4_500 / 250</gadget>
<output>18</output>

<gadget id="calculator">18 - 1 - 1</gadget>
<output>16</output>

<gadget id="calculator">4_750 / 16</gadget>
<output>2_375/8 = around 296.875</output>

<result>2_375/8 = around 296.875</result>