设：酒瓶数量为n,直径d
绳子长度=nd+πd=(n+π)d
2只酒瓶绳子长度=(2+3.14)*8=41.12(厘米)
3只酒瓶绳子长度=(3+3.14)*8=49.12(厘米)
4只酒瓶绳子长度=(4+3.14)*8=57.12(厘米)