\[\boxed{\mathbf{77.}}\]
\[\textbf{а)}\ (2 + 8) \cdot 3 = 30\]
\[\textbf{б)}\ ( - 4 + 8) \cdot 3 = 12\]
\[\textbf{в)}\ (5,2 + 8) \cdot 3 = 13,2 \cdot 3 = 39,6\]
\[\textbf{г)}\ ( - 9,1 + 8) \cdot 3 =\]
\[= - 1,1 \cdot 3 = - 3,3\]