\[\boxed{\mathbf{3.}\mathbf{356}}\]
\[\textbf{а)}\ 256\ :2 = 128\]
\[256\ :4 = 64\]
\[256\ :8 = 32\]
\[256\ :16 = 16\]
\[256\ :64 = 4\]
\[256\ :128 = 2\]
\[\textbf{б)}\ 8 + 8 = 16 + 8 = 24 + 8 =\]
\[= 32 + 8 = 40\]
\[8 \cdot 5 = 40\]
\[8 \cdot 3 = 24\]