Answer:
2.9m/s
Step-by-step explanation:
Given parameters: 
Mass 1 = 87kg 
Speed 1 = 2.6m/s 
Mass 2 = 78kg 
Unknown: 
Speed 2 = ? 
Solution: 
Momentum is the amount of motion a body possesses. 
 Momentum = mass x velocity 
 Momentum of skater 1 = Momentum of skater 2 
 So; 
 87 x 2.6 = 78 x speed 2 
 Speed 2 = 2.9m/s