3) log256 + 2 log2 12 log2 63.

3) $$log_2 56 + 2log_2 12 - log_2 63 = log_2 56 + log_2 12^2 - log_2 63 = log_2 \frac{56 \cdot 144}{63} = log_2 \frac{8 \cdot 7 \cdot 16 \cdot 9}{9 \cdot 7} = log_2 (8 \cdot 16) = log_2 2^3 \cdot 2^4 = log_2 2^7 = 7$$

Ответ: 7