Xiaohong went to her aunt's house. If you take a car back and forth, it will take 20 minutes on the road; if you take a car when you go there and walk when you come back, it will take a total of 50 minutes. How many minutes does it take Xiaohong to walk back?
小红到姑妈家．如果来回都乘车，那么路上要用20分钟；如果去时乘车，回来时步行，那么一共要用50分钟．小红步行回来要用多少分钟．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">50 - 10</gadget>
<output>40</output>

<result>40</result>