\[\boxed{\text{6.346.}}\]
\[\textbf{а)}\ 78 \cdot 0,16 = (78 \cdot 16)\ :100\]
\[78 \cdot (16\ :100) = (78 \cdot 16)\ :100\]
\[(78 \cdot 16)\ :100 = (78 \cdot 16)\ :100.\ \]
\[\textbf{б)}\ 0,037 \cdot 0,3 = (37 \cdot 3)\ :10\ 000\]
\[(37\ :1\ 000) \cdot (3\ :10) =\]
\[= (37 \cdot 3)\ :10\ 000\ \]
\[(37 \cdot 3)\ :(1\ 000 \cdot 10) =\]
\[= (37 \cdot 3)\ :10\ 000\]
\[(37 \cdot 3)\ :10\ 000 =\]
\[= (37 \cdot 3)\ :10\ 000.\ \ \]