Solution
= Solution
For $x\ne0$, the <integrating factor> for $y'-y/x=3$ can be taken as $1/x$ on either half-line. Thus $(y/x)'=3/x$, giving
$$
\boxed{y=x\bigl(C+3\ln|x|\bigr).}
$$
The arbitrary constant may differ on the disconnected domains $x>0$ and $x<0$.