Centre of mass — UPSC CSE 1997 Physics PYQ

In the ammonia molecule the three hydrogen atoms form an equilateral triangle. The distance between the centre of this triangle from each hydrogen atom is 0.939\text{ \AA}. The nitrogen atom is at the apex of the pyramid with the three hydrogen atoms forming the base. The distance between the hydrogen and nitrogen atoms is 1.014\text{ \AA}. Find the position of the centre of mass relative to the nitrogen atom.