(2^2.a^3)^3×(2a^2.a^-5)

(2^2 . a^3)^3 . (2a^2 . a^-5)
= 2^2(3) . a^3(3) . 2 . a^(2 + (-5))
= 2^6 . a^9 . 2 . a^-3
= 64 . 2 . a^(9 + (-3))
= 128 a^6