Connecting multiple billy bookcases

[Jaymig926]

Hello all I'm purchasing two 31 1/2" wide Billies and one 15 inch wide Billy (they are all 41 inches high).
how do I connect them all side by side to each other so I don't have gaps in between each one?
Thanks to all in advance

 

[316what]

They should come with hardware/brackets to connect on the top.