Velocity of c.m of the system is given as
→vcm=m1→v1+m2→v2m1+m2
Since the particles m1 and m2 are moving unidireactionally
m1→v1 and m2→v2 are parallel
⇒∣∣m1→v1+m2→v2∣∣=m1v1+m2v2
Therefore vcm=m1→v1+m2→v2m1+m2=|m1v1+m2v2|m1+m2=(1)(2)+(1/2)(6)(1+12)m/s=3.33m/sec