(-1/42)/(-2/7+1/6-3/14+2/3)
=(-1/42)/(-2/7)+(-1/42)/(1/6)-(-1/42)/(3/14)+(-1/42)/(2/3）
=-7/84-1/7+43/126-18/84
=-25/84-18/126+43/126
=-25/84-25/126
=-75/252-50/252
=-125/252