Ralph, (f + g)(1) is shorthand for f(1) + g(1).
(f + g)(1) = 1 + 6 + 1 - 3 = 5
If you are diving the two, then the only thing we can't do is have the denominator = 0.
2x + 3 = 0
2x = -3
x = -3/2
So, the domain is all real numbers except -3/2.