The students rowed the boat along the river, traveling 3.5 kilometers per hour, and reached the other side of the river in 4.2 hours. When returning, paddle against the current and travel 2.94 kilometers per hour. How many hours can you return to the original place?
同学们划着小船顺水而行，每小时行3.5千米，4.2小时到达河对岸．返回时逆水划行，每小时行2.94千米，几小时可返回原地？
<gadget id="calculator">4.2 / 2.94</gadget>
<output>1.428571</output>

<gadget id="calculator">3.5 * 1.428571</gadget>
<output>4.999999</output>

<result>4.999999</result>