The domain is what values x can be. Fractions are undefined if the denominator is zero. ** I'm going to assume only the 3x is in the denominator and NOT (3x-3). Answers will be different if this isn't the case.
If only 3x is in the denominator then x is all real numbers except x ≠ 0
The range is all values y can take on. This shows the overall behavior of the graph. Picture what happens if x → ∞ (gets really really big).. Since it's in the denominator the fraction get's really really small. It approaches zero leaving nothing but y = - 3 as an asymptote. So y is all real numbers except y ≠ -3