(21 a^9 c^7)^-½

(81 a^5 b^6 c)^-½

I ended up with √((27b^6)/(7a^4c^6)) but I get the feeling I'm not doing it correctly.

(-2 a^-1 b^6)^3

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

I don't even know where to start with this equation. How would I solve this?

Thanks!