The equation of a circle is: (x - xo)^2 + (y - yo)^2 = r^2
Where xo and yo are the coordinates of the center = (3,4).
r is the radius of the circle and you can find it using the equation of the distance between the point (-3,-4) and the center (3,4):
r^2 = (-3 -3)^2 + (-4 - 4)^2 = 6^2 + 8^2 = 36 + 64 = 100.
=> r = √100
=> r = 10
Answer: r = 10