A coal truck drove from A to B at an average speed of 40 kilometers per hour for 7.5 hours. After arriving at B, it took 5 hours to unload the coal and return the truck. What is the average speed of the truck going back and forth?
一辆运煤的货车从甲地开往乙地，以平均每小时40千米的速度行驶了7.5时，到达乙地后，卸下煤，货车返程，用了5时．货车往返的平均速度是多少？
<gadget id="calculator">40 * 7.5 * 2</gadget>
<output>600</output>

<gadget id="calculator">7.5 + 5</gadget>
<output>12.5</output>

<gadget id="calculator">600 / 12.5</gadget>
<output>48</output>

<result>48</result>