The distance between the two ports A and B is 560 kilometers. It takes 105 hours for Ship A to go back and forth between the two ports. Among them, sailing upstream takes 35 hours longer than sailing downstream. The speed of Ship B in still water is twice that of Ship A in still water. How many hours does it take to go back and forth between the two ports?
A、B两港相距560千米，甲船在两港间往返一次需105小时，其中逆流航行比顺流航行多用了35小时，乙船的静水速度是甲船静水速度的2倍，乙船在两港间往返一次需要多少小时？
<gadget id="calculator">105 - 35</gadget>
<output>70</output>

<gadget id="calculator">70 / 2</gadget>
<output>35</output>

<gadget id="calculator">560 / 35</gadget>
<output>16</output>

<gadget id="calculator">560 / 70</gadget>
<output>8</output>

<gadget id="calculator">16 - 8</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">24 - 4</gadget>
<output>20</output>

<gadget id="calculator">560 / 20</gadget>
<output>28</output>

<gadget id="calculator">24 + 4</gadget>
<output>28</output>

<gadget id="calculator">560 / 28</gadget>
<output>20</output>

<gadget id="calculator">28 + 20</gadget>
<output>48</output>

<result>48</result>