A tourist rented a boat at the pier at 9:00 a.m., and he had to return to the pier by 12:00 a.m. according to regulations. It is known that the speed of the boat in still water is 5 kilometers per hour and the speed of the river is 2 kilometers per hour. Tourists have to rest for 10 minutes every half hour. They are not allowed to change direction halfway, and they start to row back just after a break. How many kilometers can the tourist travel farthest from the pier?
一游客上午9时在码头租了一条小船划出，按规定他必须在12时之前回到码头．已知小船的静水速度是每小时5千米，河水流速是每小时2千米．游客每划半小时就要休息10分钟，中途不允许改变方向，并且恰好在某次休息后开始往回划．这位游客最远可划离码头多少千米．
<gadget id="calculator">23 / 6</gadget>
<output>23/6 = around 3.833333</output>

<result>23/6 = around 3.833333</result>