River A is a tributary of River B. The speed of water in River A is 3 kilometers per hour, and the speed of water in River B is 2 kilometers per hour. A boat sails along River A for 7 hours, travels 133 kilometers to reach River B, and sails upstream for 84 kilometers on River B. How many hours does the boat have to travel?
A河是B河的支流，A河水的水速为每小时3千米，B河水的水流速度是2千米．一船沿A河顺水航行7小时，行了133千米到达B河，在B河还要逆水航行84千米，这船还要行多少小时．
<gadget id="calculator">133 / 7</gadget>
<output>19</output>

<gadget id="calculator">19 - 3</gadget>
<output>16</output>

<gadget id="calculator">16 - 2</gadget>
<output>14</output>

<gadget id="calculator">84 / 14</gadget>
<output>6</output>

<result>6</result>