\[1)\ 7\ :\frac{7}{8} = \frac{7 \cdot 8}{7} = 8.\]
\[2)\ a\ :12 = 8 \Rightarrow a = 96.\]
\[2)\ b\ :4 = 8 \Rightarrow b = 32.\]
\[Ответ:a = 96;\ \ b = 32.\]