Xiao Li and Xiao Chen are traveling westward from West Village and East Village respectively. Xiao Li rides a bicycle and travels 15 kilometers per hour, Xiao Hong walks 3 kilometers per hour, and Xiao Ming catches up with Xiao Hong after 3 hours. How many kilometers apart?
小李和小陈分别从西村和东村同时向西而行，小李骑自行车每小时行15千米，小红步行每小时行3千米，3小时后小明追上小红，求东西村相距多少千米？
<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<result>36</result>