A car goes back and forth between A and B with a speed of 52 km/h, takes 3 hours, and only takes 4 hours to return. What is the speed of this car when it returns?
一辆汽车往返于甲、乙两地，去时的速度为52千米/时，共用3小时，返回时只用了4小时，这辆汽车返回时的速度是多少？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">52 * (3/4)</gadget>
<output>39</output>

<result>39</result>