$(\frac{6+7+8}{5}-\frac{7+8+9}{6}+\frac{8+9+10}{7}-\frac{9+10+11}{8})/(\frac{1}{5}-\frac{1}{6}+\frac{1}{7}-\frac{1}{8})$ 这怎么简便运算啊？？？在线等，急！！！！！