Answer: Vcm = m1v1 + m2v2 / m1 + m2
Explanation:
The distance of centre of mass Xcm can be taken by taking mass moments about the origin.
(m1 + m2)Xcg = m1x1 + m2x2
Xcm = m1x1 + m2x2 / m1 + m2
Differentiating Xcm = m1x1 + m2x2 / m1 + m2 with respect to time t, will give us the velocity of the centre of mass.
I have attached a diagram showing said differentiation.