JEE Advanced Model Paper 1 with solutions for online practice

The centers of two circles C1 and C2 each of unit radius are at a distance of 6units from each other. Let P be the midpoint of the lines segment joining thecenters of C1 and C2 and C be a circle touching circles C1 and C2 externally. Ifa common tangent to C1 and C2 passing through P is also a common tangent to C2 and C , then the radius of circle C is