We start with the expression:
\[
\frac{15 y + 39}{y^{2} + 4 y} \cdot \frac{y + 4}{5 y + 13}
\]
First, we factor the numerator \(15 y + 39\) and the denominator \(y^{2} + 4 y\):
The numerator can be factored as:
\[
15 y + 39 = 3(5 y + 13)
\]
The denominator can be factored as:
\[
y^{2} + 4 y = y(y + 4)
\]
Step 2: Rewrite the Expression
Substituting the factored forms back into the expression, we have:
\[
\frac{3(5 y + 13)}{y(y + 4)} \cdot \frac{y + 4}{5 y + 13}
\]
Step 3: Cancel Common Factors
Next, we can cancel the common factors in the numerator and denominator:
The factor \(5 y + 13\) in the numerator of the first fraction and the denominator of the second fraction cancels out.
The factor \(y + 4\) in the numerator of the second fraction and the denominator of the first fraction also cancels out.
After canceling, we are left with:
\[
\frac{3}{y}
\]
Step 4: Final Simplified Expression
The final simplified expression is:
\[
\frac{3}{y}
\]