First you must realize that the domain is restricted for c(x), in that division by zero is undefined, so x cannot equal 2. Realizing this before you start is important because the final form of (cd)(x) may appear to not have that restriction, but having x=2, would still have no meaning regardless of what (cd)(x) becomes.
(cd)(x)=5(x+3)/(x-2)
(cd)(x)=(5x+15)/(x-2)
Now we can see that the same restriction applies to the composite function, so the domain is: x=(-oo, 2)U(2, +oo). "All real numbers except two."