原式=6/7÷[7/8-7/12+1/8]=6/7÷[1-7/12]=6/7÷5/12=6/7x12/5=72/35=2(2/35)即：二又三十五分之二
7/8-7/12+1/8 =1-7/12=5/12 6/7/5/12=72/35
