It takes a car 3.4 hours to go up the mountain and 2.6 hours to go down the mountain. It is known that the distance from the foot of the mountain to the top of the mountain is 78 kilometers. What is the average speed of going up and down the mountain in kilometers?
一辆汽车上山时用了3.4小时，下山时用了2.6小时，已知山脚到山顶的路程是78千米，上下山的平均速度是多少千米？
<gadget id="calculator">3.4 + 2.6</gadget>
<output>6</output>

<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">78 * (1/3)</gadget>
<output>26</output>

<result>26</result>