\[\boxed{\mathbf{3.}\mathbf{228}}\]
\[\textbf{а)}\ 8 \cdot 46 \cdot 125 = 46 \cdot (8 \cdot 125) =\]
\[= 46 \cdot 1000 = 46\ 000\]
\[\textbf{б)}\ 24 \cdot 13 \cdot 125 =\]
\[= 3 \cdot 8 \cdot 13 \cdot 125 =\]
\[= (3 \cdot 13) \cdot (8 \cdot 125) =\]
\[= 39 \cdot 1000 = 39\ 000\]
\[\textbf{в)}\ 71 + 785 + 94 + 29 + 215 =\]
\[= (71 + 29) + (785 + 215) + 94 =\]
\[= 100 + 1000 + 94 = 1194\ \]