A circle `C_(1)` has radius 2 units and a circles `C_(2)` has radius 3 units. The distance between the centres of `C_(1)` and `C_(2)` is 7 units. If two points, one tangent to both circles and the other passing through the centre of both circles, intersect at point P which lies between the centers of `C_(1) and C_(2)`, then the distance between P and the centre of `C_(2)` is