Step 1: Use the factor theorem
If \( (x+3) \) is a factor, then substituting \( x = -3 \) in \( ax^2 + x + 1 \) should yield 0.
Step 2: Substitute \( x = -3 \)
\[
a(-3)^2 + (-3) + 1 = 0
\]
\[
9a - 3 + 1 = 0
\]
\[
9a - 2 = 0
\]
\[
9a = 2
\]
\[
a = \frac{2}{9}
\]
Step 3: Conclusion
Thus, the correct answer is \( \frac{2}{9} \).