Here is a second way:
 the two given points are equidistant from the center    (x, 0)
 Use distance formulas for the two points and the center
 (x-0)^2  + 4^2 = (x-1)^2 + 8^2
    solve for x = 49/2      so circle center is   49/2 , 0
  
 use one pont to solve for r in the circle formula   (0,4 )
 ( 0 - 49/2)^2 + (4-0)^2 = r^2
    r^2 = 616.25                       r = sqrt (616.25)