River A is a tributary of River B. The speed of River A is 3 kilometers per hour, and the speed of River B is 2 kilometers per hour. A boat travels along River A for 7 hours and arrives at River B, sailing a total of 133 kilometers. How many hours does it take for the boat to sail upstream for 84 kilometers on the Yi River?
甲河是乙河的支流，甲河水速为每小时3千米，乙河水速为每小时2千米．一艘船沿甲河顺水7小时后到达乙河，共航行133千米．这艘船在乙河逆水航行84千米，需要花多少小时？
<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>