а) $$4^{11} \cdot 4^{-9} = 4^{11-9} = 4^2 = 16$$
б) $$6^5 : 6^{-3} = 6^{5-(-3)} = 6^{5+3} = 6^8 = 1679616$$
в) $$(2^{-2})^3 = 2^{-2 \cdot 3} = 2^{-6} = \frac{1}{2^6} = \frac{1}{64} = 0.015625$$
Ответ: a) 16; б) 1679616; в) 0.015625