ANSWER
[tex]f(a + 2) = \frac{a + 5}{a - 1} [/tex]
EXPLANATION
The given function is
[tex]f(x) = \frac{3 + x}{x - 3} [/tex]
To find f(a+2) we substitute x=a+2.
That is wherever we see 'x' we replace it with 'a+2'
[tex]f(a + 2) = \frac{3 + a + 2}{a + 2 - 3} [/tex]
We simplify further to obtain:
[tex]f(a + 2) = \frac{a + 5}{a - 1} [/tex]
This is defined for
[tex]a \ne1[/tex]