A and B are 160 kilometers apart. The speed of a ship in still water is 30 km/h and the speed of water is 10 km/h. How many hours does it take for the ship to go back and forth between the two ports?
A、B两港相距160千米，一只船的静水速度是30千米/时，水流速度是10千米/时，那么这只船在两港间往返一次需要多少小时？
<gadget id="calculator">30 + 10</gadget>
<output>40</output>

<gadget id="calculator">160 / 40</gadget>
<output>4</output>

<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<gadget id="calculator">160 / 20</gadget>
<output>8</output>

<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<result>12</result>