Hi Sibani dear,
First of all we could simplify as( a^3* x^2 /3 )^3
(Recall 1/x^-n = x^n)
Now power 3 would be distributed to each
So a^9 * x^6 / 3^3 = a^9 * x^6 / 27
ii) In this case too we can simplify as 2/3 * a^5 / b^6)^-2
Because of - ve sign in power we can reciprocate the factors within
So we get (3/2 * 1/a^5 * b^6 )^2
Distributing the power 2 we get 9/4 * 1/a^10 * b^12