We start with the given rational expressions:
\[
\frac{(x-y)^{2}}{x+y} \quad \text{and} \quad \frac{3x+3y}{y^{2}-y^{2}}
\]
Step 2: Analyze the Denominator
The second expression has a denominator of \(y^{2} - y^{2}\), which simplifies to \(0\). This indicates that the expression is undefined for all values of \(y\), leading to a division by zero.
Step 3: Multiply the Expressions
Despite the second expression being undefined, we can still multiply the numerators:
\[
\text{Numerator: } 3x + 3y = 3(x + y)
\]
Thus, the multiplication of the two expressions results in:
\[
\frac{(x-y)^{2} \cdot 3(x+y)}{0}
\]
Step 4: Simplify the Result
The overall expression simplifies to:
\[
\frac{3(x-y)^{2}(x+y)}{0}
\]
Since the denominator is \(0\), the entire expression is undefined, leading to the conclusion that the result is:
\[
\text{Simplified: } \text{zoo} \cdot (x - y)^{2} \cdot (x + y)
\]
This indicates that the expression does not have a valid value in its domain due to the division by zero.