That is$,$ level curves F$($x$,$ y$)=$ C

are solutions to the differential equation:

dy

dx $=3$x$23$y

$$x $+$ y$4$

First rewrite as

M$($x$,$ y$)$ dx $+$ N$($x$,$ y$)$ dy $=0$

where M$($x$,$ y$)=,$

and N$($x$,$ y$)=$