a, Để \(y=\left(a-4\right)x+5//y=3x+2\)
\(\Leftrightarrow\left\{{}\begin{matrix}a-4=3\\5\ne2\end{matrix}\right.\Leftrightarrow a=7\)
b, Thay \(x=2;y=-4\Leftrightarrow-4=2a+b\)
Thay \(x=-1;y=5\Leftrightarrow-a+b=5\)
\(\Leftrightarrow\left\{{}\begin{matrix}2a+b=-4\\b-a=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=-3\\b=2\end{matrix}\right.\)