-1/63/(3/14-2/9+1/7-1/3)
=-1/[63x(3/14-2/9+1/7-1/3)]
=-1/(63x3/14-63x2/9+63x1/7-63x1/3)
=-1/(13.5-14+9-21)
=-1/(-12.5)
=2/25