A unit of the People’s Liberation Army had to march 502 kilometers for military training. At the beginning, they walked 60 kilometers a day. After walking for 3 days, they walked 20.5 kilometers a day for the remaining distance. How many days will it take for the rest of the journey?
解放军某部队进行军事训练，要行军502千米，开始每天走60千米，走了3天后，余下的路程每天多走20.5千米．余下的路程还需要几天才能走完？
<gadget id="calculator">60 * 3</gadget>
<output>180</output>

<gadget id="calculator">502 - 180</gadget>
<output>322</output>

<gadget id="calculator">60 + 20.5</gadget>
<output>80.5</output>

<gadget id="calculator">322 / 80.5</gadget>
<output>4</output>

<result>4</result>