Let  (h, k)  be the center of the circle
  
 And the distance  from this point to each  of the points  will be  equal  (the radius)
  
 So  we have this equation
  
 ( h - - 7)^2  + (k - 0)^2  =  ( h  - 7)^2  + (k - 0 )^2
 (h + 7)^2    =  ( h - 7)^2
 h^2 + 14h + 49  =  h^2 - 14h + 49
 14h  =  - 14 h
 28h  = 0
 h  = 0
  
 And we can solve for k, thusly
  
 (0 - 7)^2  + ( k -0)^2  =   ( 0  - - 3)^2  + (k - 4)^2
 49  + k^2  =  9  + k^2 - 8k + 16
 49  = 25  - 8k
 8k  =  25  - 49
 8k  = - 24
 k  = -3
  
 So......the center of the circle  is   ( 0, - 3)
  
 And the radius  is  given by  √  [ (0 - 7)^2  + ( -3 - 0)^2 ]  =  √ [ 49 + 9] = √58
  
 So... the equation  of  the circle is
  
 (x - h)^2  + ( y - k)^2  = r^2
  
 ( x - 0)^2  +  ( y  - - 3)^2  = 58
  
 x^2   +  ( y + 3)^2  = 58
  
  
 Here is a pic :  https://www.desmos.com/calculator/m2ugumny98
  
  
 