Answer:
The total momentum after collision = 60 kgm/s
Step-by-step explanation:

Before the collision:
Matt was moving 3 m/s to the east and Trey was moving 2 m/s to the west

According to the principle of momentum conservation:
The total momentum before collision = The total momentum after collision

Since the total momentum before collision = Total momentum after collision
The total momentum after collision = 60 kgm/s