(-1/42)/(1/6-3/14+2/3-2/7)
=(-1/42)/(1/6+2/3-3/14-2/7)
=(-1/42)/[(1/6+2/3)-(3/14+2/7)]
=(-1/42)/[5/6-1/2]
=(-1/42)/[1/3]
=-1/42*3
=-1/14