The equation of the given circle is x2+y2−6x−8y+21=0.
The center of the circle is C(3,4) and its radius is r=32+42−21=4=2.
The equation of the given parabola is x2+6x+y+13=0.
Rewriting the equation by completing the square, we get (x+3)2=−(y+4).
The vertex of the parabola is V(−3,−4).
The maximum distance of a moving point P on the circle from the vertex V is given by CV+r.
The distance between the center C(3,4) and the vertex V(−3,−4) is CV=(3−(−3))2+(4−(−4))2=62+82=100=10.
Therefore, the maximum distance is 10+2=12.
Answer: 12