simplify completely: (3a^3b )-3

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( 2a^-1b^2)

I am assuming the numerator is to the power of -3

numerator becomes 1/3 * a^0 * 1/b^3= 1/3b

denominator is 2b^2/a

putting it together

numerator * 1/denominator

1/3b * a/2b^2= a/6b^3