The distance between two ports, A and B, is 77 kilometers, the speed of the ship is 9 kilometers per hour, and the speed of the water is 2 kilometers per hour. How many hours does it take to sail from port A to port B along the water?
甲、乙两个港口相距77千米，船速为每小时9千米，水流速度为每小时2千米，那么由甲港到乙港顺水航行需多少小时．
<gadget id="calculator">9 + 2</gadget>
<output>11</output>

<gadget id="calculator">77 / 11</gadget>
<output>7</output>

<result>7</result>