$$\frac{11a^6b^3 - (3a^2b)^3}{4a^6b^6} = \frac{11a^6b^3 - 27a^6b^3}{4a^6b^6} = \frac{-16a^6b^3}{4a^6b^6} = -\frac{4}{b^3}$$
При $$b = 2$$:
$$- \frac{4}{2^3} = - \frac{4}{8} = - \frac{1}{2} = -0.5$$
Ответ: -0.5