Lavatory Drain

I am helping my son in law install a bathroom in his basement that was plumbed with drain and water lines when the house was built 2 years ago. The toilet and tub were no problem. Where I do have a problem is with the drain for the lavatory. The floor drain is centered between the water lines. Because they went with a 48" lavatory, it puts the center of the lavatory drain about 18" from the floor drain pipe. What is the correct way to deal with this? Do I put the trap directly under the lavatory drain then run a horizontal pipe over to the floor drain and elbow it down at that point, or do I com down from the lavatory draw, install an elbow and run horizontally over to a trap and striaght down to the floor drain? Any help would be appreciated.

Jerry

Actually NEITHER, without a vent the drain will NEVER operate properly. Whoever installed the drain, (and, the trap should be under the sink, NOT be under the floor), should have put it in the wall with a vent going upward, OR it was installed that way, but you moved the wall so the pipes are under the sink and could not continue the vent the way it was designed.