A car drives from place A to place B, travels an average of 87 kilometers per hour, and takes 4 hours to reach the destination. It takes 6 hours to come back, what is the average speed of this car going back and forth between the two places?
一辆汽车由甲地开往乙地，去时平均每小时行驶87千米，用了4小时到达目的地．回来时用6小时，求这辆汽车往返两地的平均速度是多少？
<gadget id="calculator">6 + 4</gadget>
<output>10</output>

<gadget id="calculator">2 / 10</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">87 * 4 * (1/5)</gadget>
<output>348/5 = around 69.6</output>

<result>348/5 = around 69.6</result>