A cargo ship departs from a port at 10:00 am, and a passenger ship departs from this port at 2:00 pm along the route of the cargo ship. The passenger ship catches up with the cargo ship within 6 hours. The speed of the passenger ship is 40 kilometers per hour.
上午10时从一个港口开出一艘货船，下午2时又从这个港口开出一艘客船沿货船航线行驶，客船开出6小时追上货船，客船时速40千米，货船时速多少千米．
<gadget id="calculator">4 + 6</gadget>
<output>10</output>

<gadget id="calculator">6 / 10</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">40 * (3/5)</gadget>
<output>24</output>

<result>24</result>