A cargo ship sails from the east port to the west port, travels 15 kilometers per hour along the water, and can reach it in 8 hours. From Xigang to Donggang, due to the upstream, the travel time is 3 kilometers less than that of the downstream, so how many hours can you reach Donggang?
一只货船从东港驶向西港，顺水每小时行15千米，8小时可以到达．从西港返回东港由于逆水，每小时比顺水少行3千米，这样多少小时可以到达东港？
<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<gadget id="calculator">8 / 12</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">15 * (2/3)</gadget>
<output>10</output>

<result>10</result>