The function is
[tex]y=\frac{2}{3+x}[/tex]Remember that, for y to be a number, we cannot have things of the form
[tex]\begin{gathered} \frac{1}{0},\frac{2}{0},\ldots \\ \frac{1}{0},\frac{2}{0},\ldots\notin\mathfrak{\Re } \end{gathered}[/tex]Therefore, we always need to avoid this kind of result.
We can see that the only way 'y' acquires a value like that is if
[tex]\begin{gathered} 3+x=0 \\ \Rightarrow x=-3 \end{gathered}[/tex]Therefore, y is well for any value of x, except when x=-3.
Thus, the domain of the function y (y(x)) is
[tex]x\in(-\infty,-3)\cup(-3,\infty)=\mathfrak{\Re }-\mleft\lbrace-3\mright\rbrace[/tex]The domain of y is all the numbers except for -3