To solve this problem we will use the concept related to the center of mass by speed of two objects that approach each other.
According to the information our values are
Stationary
The center of mass of the two particles is
Replacing,
Therefore the speed does the heavier particle approach the center of mass of two particles is -0.6109m/s (From the reference system this speed can be taken as negative. As the lightest mass (our reference system) is receiving the impact of the heaviest mass)