First, factor the numerator and the denominator of the given expression.
The numerator is:
\[
u^{2} + 3u + 2
\]
This can be factored as:
\[
(u + 1)(u + 2)
\]
The denominator is:
\[
3u^{2} - 12
\]
Factor out the greatest common factor (GCF), which is 3:
\[
3(u^{2} - 4)
\]
Now, factor \(u^{2} - 4\) as a difference of squares:
\[
3(u - 2)(u + 2)
\]
Step 2: Rewrite the expression with factored forms
Substitute the factored forms of the numerator and denominator back into the original expression:
\[
\frac{(u + 1)(u + 2)}{3(u - 2)(u + 2)}
\]
Step 3: Cancel common factors
Notice that \((u + 2)\) appears in both the numerator and the denominator. Cancel this common factor:
\[
\frac{u + 1}{3(u - 2)}
\]
Final Answer
The simplified form of the expression is:
\[
\boxed{\frac{u + 1}{3(u - 2)}}
\]