Answer with Explanation:
We are given that
Mass of one body=4.5 kg
Initial velocity of one body=8.9 m/s
Initial velocity of another body=0
Final velocity of one body=

a.We have to find the mass of the other body.
Energy and momentum are conserved in this system


(equation I)
From conservation of kinetic energy

(equation II)
Substitute equation I in equation II


Substitute the given values then we get


Hence, the mass of other body=3 kg
b.We have to find the speed of two body center of mass .
The center of mass speed is given by

Substitute the values then we get


Hence, the speed of the two body center of mass is given by =5.34 m/s