The distance between the two piers is 192 kilometers. It takes 8 hours for a motorboat to travel along the water. Given that the current speed is 4 kilometers per hour, how many hours will it take to travel upstream.
两个码头相距192千米，一艘汽艇顺水行完全程要8小时，已知水流速度是每小时4千米，逆水行完全程要用多少小时．
<gadget id="calculator">192 / 8</gadget>
<output>24</output>

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

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">192 / 16</gadget>
<output>12</output>

<result>12</result>