A car goes up a mountain at a speed of 45 kilometers per hour, walks for 4 hours to reach the destination, and then goes downhill by another road at a speed of 60 kilometers per hour, and travels for 2 hours to reach the bottom of the mountain. What is the average time for this car to go up and down the mountain? What is the speed?
一辆汽车上山的速度是每小时45千米，行走4小时到达目的地，然后从另一条路下山，下山速度每小时60千米，车行2小时到山脚，问这辆车上下山的平均速度是多少？
<gadget id="calculator">45 * 4</gadget>
<output>180</output>

<gadget id="calculator">60 * 2</gadget>
<output>120</output>

<gadget id="calculator">180 + 120</gadget>
<output>300</output>

<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<gadget id="calculator">300 / 6</gadget>
<output>50</output>

<result>50</result>