So this is what we got
-(2/3a)^4
So imagine the 2/3 and a have an imaginary ^1 so it is really
-( 2/3^1 a^1 )^4
so you take the exponet 4 and times it by the other exponets on 2/3 and a
Your final anwser is
-16/81a^4 i believe
someone please correct me if im wrong