\[\boxed{\mathbf{3.}\mathbf{309}}\]
\[\textbf{а)}\ 10^{2}\ :\left( 6^{2} + 2^{6} \right) =\]
\[= 100\ :(64 + 36) =\]
\[= 100\ :100 = 1\]
\[\textbf{б)}\ \left( 10^{2} - 4^{3} \right) \cdot 3^{3} =\]
\[= (100 - 64) \cdot 27 = 36 \cdot 27 =\]
\[= 972\]
\[\textbf{в)}\ 2 \cdot 6^{3} - 7^{3} = 2 \cdot 216 - 343 =\]
\[= 432 - 343 = 89\]
\[\textbf{г)}\ 4 \cdot 3^{4} + 2^{8} = 4 \cdot 81 + 256 =\]
\[= 324 + 256 = 580\ \]