To perform polynomial addition, we combine like terms. Let's analyze the given example:
\[ (2x^2 + 6x + 1) + (3x^2 + 3x + 9) \]
Now we can group and add the coefficients of similar terms:
- \(2x^2 + 3x^2 = (2 + 3)x^2 = 5x^2\)
- \(6x + 3x = (6 + 3)x = 9x\)
- \(1 + 9 = 10\)
Putting it all together, we have:
\[ (2x^2 + 6x + 1) + (3x^2 + 3x + 9) = 5x^2 + 9x + 10 \]
Therefore, the correct answer is:
(2x^2 + 6x + 1) + (3x^2 + 3x + 9) = 5x^2 + 9x + 10.