Final answer:
The common denominator of the complex fraction is 3y.
Step-by-step explanation:
To find the common denominator of the complex fraction, we need to find the least common multiple (LCM) of the denominators.
The denominators are 3 and 3y. The LCM of 3 and 3y is 3y, since the factor y is unique to the denominator 3y.
Therefore, the common denominator of the complex fraction is 3y.