I deliberately drew the original diagram misleadingly so to not give the game away, but the fact that AB and CD are equal means that EF and GH are also equal, and that a line drawn between the centres of the top and right circles will be at 45 degrees downwards. It also follows that the line FG will be tangent to the top and right circles, and so will be equal in length to the line joining their centres. Since this is simply twice the unit radius, the length of FG will be 2.