I'm having trouble with these problems.. Could someone please explain how to find the domain of either of these functions?

3. f(x) =(x-2)/(x^2+6x+8)

7. g(x)= sqrt[(9)/(x+3)]

3. trouble arises when you divide by zero, so

consider x^2 + 6x + 8 = 0
(x+2)(x+4) = 0
x = -2, or x = -4

so for #3, domain is any real number except x = -2, -4

7.
g(x) = √( 9/(x+3))
double whammy,
we can' divide by zero, and we can't take √ of a negative
when is 9/(x+3) negative or zero?
when x ≤ -3

so domain:
any x , such that x > -3