River A is a tributary of River B. The water speed of River A is 3 kilometers per hour, and the speed of River B is 2 kilometers per hour. A boat sails along River A for 7 hours and arrives at River B. How long does it take for the ship to sail upstream for 84 kilometers in the Yi River?
甲河是乙河的支流，甲河的水速为3千米每小时，乙河的水速为2千米每小时，一艘船沿着甲河顺水航行7小时后到达乙河，一共航行了133千米，这艘船在乙河中逆水航行84千米需要多少时间？
<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>