The school organized a spring outing. The students set off at one o'clock in the afternoon, walked a flat road, climbed a mountain, and then returned on the same road, and returned to school at seven o'clock in the afternoon. It is known that their walking speed is 4 km/h on the flat ground, 3 km/h on the uphill, and 6 km/h on the downhill. Question: How much did they walk in total?
学校组织春游，同学们下午一点出发，走了一段平坦的路，爬了一座山，然后按原路返回，下午七点回到学校．已知他们的步行速度平地为4千米/时，上山为3千米/时，下山为6千米/时．问：他们一共走了多少路？
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

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

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/3) + (1/6)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 / (1/2)</gadget>
<output>4</output>

<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<result>24</result>