\[\boxed{\mathbf{78.}}\]
\[\textbf{а)}\ 2 \cdot 3 + 8 = 6 + 8 = 14\]
\[\textbf{б)} - 4 \cdot 3 + 8 = - 12 + 8 = - 4\]
\[\textbf{в)}\ 5,2 \cdot 3 + 8 = 15,6 + 8 = 23,6\]
\[\textbf{г)} - 9,1 \cdot 3 + 8 =\]
\[= - 27,3 + 8 = - 19,3\]