It takes 4 hours for a truck to drive 75 kilometers per hour from station A to station B empty. It took 6 hours to return with full goods and return by the same route. How many kilometers per hour did you drive when you returned?
一辆货车，从A站到B站空车行驶每小时75千米，用了4小时．回来时装满货物按原路返回，用了6小时，返回时每小时行驶多少千米？
<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>