Matt's Momentum After Jumping from Skateboard

[guru]

Matt is gliding on his skateboard at 4.00 m/s. He suddenly jumps backward off the skateboard, kicking the skateboard forward at 8.00 m/s. Matt's mass is 50 kg and the skateboard's mass is 7 kg. How fast is Matt going as his feet hit the ground?

I have no idea where to begin. Should I first find the change in momentum?

 

[BLaH!]

All you have to do is use conservation of momentum:

p_{final} = p_{initial}

 

[guru]

Is this right

All you have to do is use conservation of momentum:

p_{final} = p_{initial}

v_f(50kg + 7kg) = 50kg*4m/s + 7kg*4m/s
v_f = 4.49m/s ?