Three cars A, D, and C start from A to B at the same time. According to the original speed, A car should arrive 10 minutes earlier than D car. 20 minutes after they set off from place A at the same time, when it rained and the road was muddy, the speed of car A dropped (1/3), the speed of car D dropped (1/4), and the speed of car C dropped (1/5), resulting in three cars Arrive at B at the same time, so how many minutes will it take for C to travel the entire distance?
A、D、C三辆汽车同时从甲地出发到乙地去，按原定速度，A车应比D车早到10分钟．在他们同时从甲地出发20分钟后，遇上下雨道路泥泞，A车速度下降(1/3)，D车速度下降(1/4)，C车速度下降(1/5)，结果三车同时到达乙地，那么C车原定行驶完全程要用多少分钟？
<gadget id="calculator">15 / 8</gadget>
<output>15/8 = around 1.875</output>

<gadget id="calculator">(15/8) * 20</gadget>
<output>75/2 = around 37.5</output>

<gadget id="calculator">5 / 3</gadget>
<output>5/3 = around 1.666667</output>

<gadget id="calculator">(5/3) * 20</gadget>
<output>100/3 = around 33.333333</output>

<gadget id="calculator">10 - (100/3)</gadget>
<output>-70/3 = around -23.333333</output>

<gadget id="calculator">(75/2) + (-70/3)</gadget>
<output>85/6 = around 14.166667</output>

<gadget id="calculator">(15/8) - (5/3)</gadget>
<output>5/24 = around 0.208333</output>

<gadget id="calculator">(85/6) / (5/24)</gadget>
<output>68</output>

<result>68</result>