1/7[-1/5(x+2/3+12/3)-6]+8=9
1/7[-1/5(x+14/3)-6]+8=9
1/7[-1/5x-14/15-6]+8=9
-1/35x-2/15-6/7+8=9
-1/35x-14/105-90/105=9-8
-1/35x-104/105=1
-1/35x=105/105+104/105
-1/35x=209/105
x=-209/3