A big river, the water speed in the middle of the river (main channel) is 8 kilometers per hour, and the water speed along the bank is 6 kilometers per hour. A boat goes down the middle of the river and travels 520 kilometers in 13 hours. Find this boat How many hours will it take to return to the original starting point along the shore?
一条大河，河中间(主航道)水速为每小时8千米，沿岸边水速为每小时6千米，一条船在河中间顺流而下，13小时行驶520千米，求这条船沿岸边返回原出发地点，需要多少小时？
<gadget id="calculator">520 / 13</gadget>
<output>40</output>

<gadget id="calculator">40 - 8</gadget>
<output>32</output>

<gadget id="calculator">32 - 6</gadget>
<output>26</output>

<gadget id="calculator">520 / 26</gadget>
<output>20</output>

<result>20</result>