Xiaoyan rides a bicycle when she goes to school, and walks when she returns home. The journey takes 50 minutes. If you walk back and forth, the whole journey takes 70 minutes. How many minutes does it take her to cycle back and forth.
小燕上学时骑车，回家时步行，路上共用50分钟．如果往返都步行，全程需要70分钟．她往返都骑车需要多少分钟．
<gadget id="calculator">70 / 2</gadget>
<output>35</output>

<gadget id="calculator">50 - 35</gadget>
<output>15</output>

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

<result>30</result>