classmate walks to school and rides a car when returning home. It takes 80 minutes on the way; if he takes the car both times, the whole journey only takes 30 minutes; if he walks both ways, how many minutes does it take?
某同学上学时步行，回家时坐车，路上一共用了80分钟；若往返都坐车，全部行程只需要30分钟；如果往返都步行，那么需要的时间是多少分钟．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 30</gadget>
<output>15</output>

<gadget id="calculator">80 - 15</gadget>
<output>65</output>

<gadget id="calculator">2 * 65</gadget>
<output>130</output>

<result>130</result>