It is known that the distance from point A in the river to Haikou is 60 kilometers, if the boat goes down the river, it takes 4 hours to reach Haikou. It is known that the speed of the water is 6 kilometers per hour. After the boat has sailed for 4 hours, due to the high tide of the river, the speed of the water from the sea to the river is 3 kilometers per hour. How many hours will it take for the boat to return to the original place? ．
已知从河中A地到海口60千米，如船顺流而下，4小时可到海口．已知水速为每小时6千米，船返回已航行4小时后，因河水涨潮，由海向河的水速为每小时3千米，此船回到原地，还需再行多少小时．
<gadget id="calculator">60 / 4</gadget>
<output>15</output>

<gadget id="calculator">15 - 6 - 6</gadget>
<output>3</output>

<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<gadget id="calculator">60 - 12</gadget>
<output>48</output>

<gadget id="calculator">9 - 3</gadget>
<output>6</output>

<gadget id="calculator">48 / 6</gadget>
<output>8</output>

<result>8</result>