答案：$a=\dfrac{7b-8}{3}$
$\begin{array}{rcl}
\dfrac{3a+b}{8} & = & b-1 \\
3a+b & = & 8b-8 \\
3a & = & 7b-8 \\
a & = & \dfrac{7b-8}{3}
\end{array}$
$\begin{array}{rcl}
\dfrac{3a+b}{8} & = & b-1 \\
3a+b & = & 8b-8 \\
3a & = & 7b-8 \\
a & = & \dfrac{7b-8}{3}
\end{array}$
