The speed ratio of A, B, and C is: A:B=4:5, B:C=6:7. From A to B, A walks for 20 minutes, how many minutes does C have to walk?
甲，乙，丙三个人的速度的比为：甲：乙=4：5，乙：丙=6：7．从A地到B地，甲走了20分钟，丙要走多少分钟．
<gadget id="calculator">24 / 35</gadget>
<output>24/35 = around 0.685714</output>

<gadget id="calculator">20 * (24/35)</gadget>
<output>96/7 = around 13.714286</output>

<result>96/7 = around 13.714286</result>