\[\boxed{\text{6.174.}}\]
\[\textbf{а)}\ (1,9 + 4,2) \cdot 14 = 6,1 \cdot 14 =\]
\[= 85,4\]
\[\textbf{б)}\ (9,9 - 5,5) \cdot 25 = 4,4 \cdot 25 =\]
\[= 110\]
\[\textbf{в)}\ (5,21 + 3,69) \cdot 25 =\]
\[= 8,9 \cdot 25 = 222,5\ \]
\[\textbf{г)}\ (8,438 - 3,068) \cdot 12 =\]
\[= 5,37 \cdot 12 = 64,44\ \]