cement truck travels from the station to the empty cement truck at a speed of 75 km/h and travels for 4 hours. When I came back, it was full of cement, and it took 6 hours to go back the same way. How many kilometers per hour did you travel when you returned?
一辆运水泥的货车，从车站到水泥三空车行驶的速度是75千米/小时，行了4小时．回来时装满了水泥，原路返回，用了6小时．返回时每小时行多少千米？
<gadget id="calculator">4 / 6</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">75 * (2/3)</gadget>
<output>50</output>

<result>50</result>