is between A and C. A sends a letter from B to A. 8 minutes after departure, B departs from B to C. 8 minutes after B departs, C finds that A and B just took them It was upside down, so he set off from B to chase A and B by bicycle in order to transfer the letter. It is known that the speeds of A and B are equal, and the speed of C is three times the speed of A and B. If A and B have been walking during the whole process, then it will take at least 100 minutes for C to return to B from departure to transfer the letter. how many minutes.
B地在A、C两地之间，甲从B地到A地去送信，出发8分钟后，乙从B地出发到C地，乙出发8分钟后，丙发现甲、乙刚好把他们拿颠倒了，于是他从B地出发骑车去追赶甲和乙，以便把信调过来．已知：甲、乙的速度相等，丙的速度是甲乙速度的3倍，如果在整个过程中，甲乙两人一直在走，那么丙从出发到把信调过来后返到B地至少要用多少分钟．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">8 + 8 + 8 + 4 + 4</gadget>
<output>32</output>

<gadget id="calculator">32 / 2</gadget>
<output>16</output>

<gadget id="calculator">16 * 2</gadget>
<output>32</output>

<gadget id="calculator">32 + 32</gadget>
<output>64</output>

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

<gadget id="calculator">4 + 16 + 32 + 8</gadget>
<output>60</output>

<gadget id="calculator">60 / 3</gadget>
<output>20</output>

<gadget id="calculator">4 + 16 + 32 + 20</gadget>
<output>72</output>

<result>72</result>