13. Given that [tex] {x}^{2} + {y}^{2} + 10y + 16 = 0[/tex] and [tex] {(x - 3)}^{2} + {y}^{2} = 1[/tex] are two circles on the same plane. Find: a) the coordinates of the center and the radius for each circle. b) the equation of the straight line joining the center of both circles.