The school organized a spring outing. The students set off from the school at 1:00 pm, walked a flat road, climbed a mountain and then returned by the same road, and returned to school at 7:00 pm. It is known that their walking speed is 4km/hour on the flat road, 3km/hour when climbing the mountain, 6km/hour when going down the mountain, and the return time is 2.5 hours. Question: How far did they travel in total?
学校组织春游，同学们下午1点从学校出发，走了一段平路，爬了一座山后按原路返回，下午七点回到学校．已知他们的步行速度平路4km/小时，爬山3km/小时，下山为6km/小时，返回时间为2.5时．问：他们一共行了多少路？
<gadget id="calculator">7 - 1 - 3</gadget>
<output>3</output>

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

<gadget id="calculator">1 * 1</gadget>
<output>1</output>

<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">2.5 - 1</gadget>
<output>1.5</output>

<gadget id="calculator">1.5 * 4</gadget>
<output>6</output>

<gadget id="calculator">6 + 6</gadget>
<output>12</output>

<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<result>24</result>