Write the standard formula for the eqn of a circle using the info (-8,-10) about the center:
(x+8)^2 + (y+10)^2 = r^2. Next, subst. -4 for x and -2 for y. If you expand both squares on the left side and add together their magnitudes, then the sum represents the square of the radius of this circle. Can you find r^2 now? r?