A certain elementary school organized students to line up for an outing. The walking speed was 1 meter per second. Teacher Wang at the end of the line rushed to the head of the line at a speed of 2.5 meters per second, and then immediately returned to the end of the line. It took 10 seconds. How long is the line?
某小学组织学生排队去郊游，步行速度为每秒1米，队尾的王老师以每秒2.5米的速度赶到排头，然后立即返回队尾，共用了10秒钟．队伍长多少米？
<gadget id="calculator">10 * 2.5 * 2.5</gadget>
<output>62.5</output>

<gadget id="calculator">10 * 2.5</gadget>
<output>25</output>

<gadget id="calculator">25 - 25 - 10</gadget>
<output>-10</output>

<gadget id="calculator">62.5 + (-10)</gadget>
<output>52.5</output>

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

<gadget id="calculator">2.5 + 1 + 1.5</gadget>
<output>5</output>

<gadget id="calculator">52.5 / 5</gadget>
<output>10.5</output>

<result>10.5</result>