Answer:
1.8 m/s
Step-by-step explanation:
momentum = mass × velocity
initial momentum = m1v1+m2v2
 = 3×3 +2×0 = 9+0= 9 kg m/s 
let combined velocity be V 
HENCE 
final momentum = total mass × velocity 
 = (3+2) × V = 5V
According to law of conservation of momentum 
final momentum = initial momentum 
5V = 9 
V =9/5
V = 1.8 m/s