how do i figure: (-12a^2b^6)^3 over (9a^3b^9)^3

(-12a^2b^6)^3 / (9a^3b^9)^3

= ( (-12a^2b^6)/(9a^3b^9) )^3
= ( (-4/3)(1/a)(1/b^3) )^3
= (-64/27)(1/a^3)(1/b^9)
= -64/( 27a^3b^9 )