\[\boxed{\mathbf{3.}\mathbf{307}}\]
\[\textbf{а)}\ 4^{3} + 6 = 64 + 6 = 70\]
\[\textbf{б)}\ 6^{3} + 4 = 216 + 4 = 220\]
\[\textbf{в)}\ (6 + 4)^{3} = 10^{3} = 1000\]
\[\textbf{г)}\ \left( 6^{3} - 4^{3} \right)\ :(6 - 4) =\]
\[= (216 - 64)\ :2 = 152\ :2 =\]
\[= 76\ \]