Two groups of workers are painting a bridge in the bay. the first group is responsible for painting the north side of the bridge, and the second group is responsible for painting the south side of the bridge. the first group has already painted 2 kilometers of the bridge and is painting 2 additional kilometers per day. the second group has already painted 4 kilometers of the bridge and is painting 1 additional kilometer per day. when the two groups have painted the same amount of the bridge, how much of the bridge will they each have painted?