Let \( P \) be a moving point on the circle \( x^2 + y^2 - 6x - 8y + 21 = 0 \). Then, the maximum distance of \( P \) from the vertex of the parabola \( x^2 + 6x + y + 13 = 0 \) is equal to:
\( 8 \)
\( 10 \)
\( 12 \)
\( 9 \)