The car goes to the county to deliver goods. The speed is 42 km/h. It takes 4 hours. The speed when returning is 56 km/h. How many hours does it take to return?
汽车去县城送货，去时速度是42千米/时，用了4小时，返回时的速度是56千米/小时，返回时用了几小时？
<gadget id="calculator">4 / 56</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">42 * (1/14)</gadget>
<output>3</output>

<result>3</result>