See,
Since the center lies on x+y=3, take any parametric point on it as (t,3-t) as the center.
Hence equation of circle is (x-t)2+(y-3+t)2 = (3-t)2 (Since the circle touches the x axis => y cordinate of center = Radius)
Now it passes through (1,1). Put it in above and get the values of t for which the circle lies in Ist Quadrant.