The students went on field activities and walked a total of 26 kilometers. They walked on flat ground for the first 2.5 hours, with an average of 5 kilometers per hour. Later, they walked on mountainous terrain with an average of 3 kilometers per hour. How many hours did they walk in the mountains?
同学们进行野外活动，共行26千米，前2.5小时在平地上行走，平均每小时行5千米，后来在山地上行走，平均每小时行3千米，在山地行走了多少小时？
<gadget id="calculator">2.5 * 5</gadget>
<output>12.5</output>

<gadget id="calculator">26 - 12.5</gadget>
<output>13.5</output>

<gadget id="calculator">13.5 / 3</gadget>
<output>4.5</output>

<result>4.5</result>