Two beetles crawl along a circle with a circumference of 140 cm. They start from the same place at the same time in the same direction. Beetle A crawls 8 cm per minute. Beetle B turns around and crawls after crawling 30 cm, and the speed doubles. The two beetles The first encounter at a place 60 cm away from the starting point, then how many centimeters per minute did the B beetle crawl at the beginning.
两只甲虫沿一个周长为140厘米的圆爬行，它们同时从同一地点同向出发，A甲虫每分钟爬8厘米，B甲虫在爬行30厘米后调头爬行，且速度增加1倍，两只甲虫在距起点60厘米的地方第一次相遇，那么B甲虫开始时每分钟爬多少厘米．
<gadget id="calculator">140 - 60</gadget>
<output>80</output>

<gadget id="calculator">80 / 8</gadget>
<output>10</output>

<gadget id="calculator">75 / 10</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>