It takes 20 minutes for Xiaohong to go to school by bicycle, and then walk home after school. If it takes 30 minutes to walk both ways, how many minutes does it take to ride from home to school (the speed of cycling or walking remains the same).
小宏上学骑车去学校，放学步行回家，往返一次需20分；如果往返都步行需要30分，那么骑车从家到学校需要多少分(往返骑车或步行的速度不变)．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<result>5</result>