It takes 20 minutes for Xiaojun to travel to and from his grandmother's house by car. Later, it was changed to take a car when going, and walk when returning, with a total of 42 minutes. If you walk back and forth, how many points will it cost?
小军去外婆家来回都乘车要用20分．后来改为去时乘车，回来时步行，共用42分．如果步行来回，要用多少分？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">42 - 10</gadget>
<output>32</output>

<gadget id="calculator">32 * 2</gadget>
<output>64</output>

<result>64</result>