The equation, as I understand you, is
a a a b b b b b c c c c c c =a a c c c c c c /(3 b^-1)
Because b^-1 b =1 and multiplication is the opposite of division, this is equivalent to
a a a b b b b b c c c c c c =a a c c c c c c /(3 b^-1) (3 (b^-1 b) /3)
So, because multiplication only isn't affected by brackets,
a a a b b b b b c c c c c c =a a c c c c c c /(3 b^-1) (3 b^-1) b /3
So
a a a b b b b b c c c c c c =a a c c c c c c b /3
So
a a a b b b b b c c c c c c 3 /3=a a c c c c c c b /3
So
a a a b b b b b c c c c c c 3 =a a c c c c c c b
So, because the order of multiplication of any series of numbers doesn't affect the result,
a a c c c c c c b (3 a b b b b) =a a c c c c c c b 1
So
3 a b b b b =1
So
a (3 b b b b) =1 /(3 b b b b) (3 b b b b)
So
a= 1 /(3 b b b b)
So
a= 1 /(3 b^4)