a/ \(\left\{{}\begin{matrix}b=3\\a.\left(-1\right)+b=0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}b=3\\a=3\end{matrix}\right.\)
\(\Rightarrow y=3x+3\)
b/ \(\left\{{}\begin{matrix}a.1+b=2\\a.3+b=6\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}a=2\\b=0\end{matrix}\right.\)
\(\Rightarrow y=2x\)