Teacher Wang has to travel 6 kilometers from the school to the county seat. The original plan was to ride a bicycle and arrive in 20 minutes. Later, it was changed to walking, which was 200 meters less per minute than cycling. How many minutes does it take to walk to the county seat?
王老师从学校到县城，要行6千米路．原计划骑自行车，20分钟可到．后来改为步行，比骑车每分钟少行200米．步行到县城需要多用多少分钟？
<gadget id="calculator">1_000 / 20</gadget>
<output>50</output>

<gadget id="calculator">6 * 50</gadget>
<output>300</output>

<gadget id="calculator">300 - 200</gadget>
<output>100</output>

<gadget id="calculator">1_000 / 100</gadget>
<output>10</output>

<gadget id="calculator">6 * 10</gadget>
<output>60</output>

<gadget id="calculator">60 - 20</gadget>
<output>40</output>

<result>40</result>