（-1/42）/（1/6-2/7）+2/3+3/14
=（-1/42)/(7/42-6*2/42)+2/3+3/14
=（-1/42)/(-5/42)+2/3+3/14
=1/5+2/3+3/14
=3/15+2*5/15+3/14
=13/15+3/14
=(13*14+3*15)/(15*14)
=227/210它还有一次[(1/6)-(2/7)+(2/3)-(3/14)]/(-1/42),
怎么算呢？