Physics
posted by Fg .
A boy on a 2.2kg skateboard initially at rest tosses a 7.9kg jug of water in the forward direction.
If the jug has a speed of 3.2m/s relative to the ground and the boy and skateboard move in the opposite direction at .56m/s, find the boy's mass.
Answer in units of kg.

initial momentum= final momentum
0=(M+2.2).56+7.9(3.2)
solve for M 
24.048 kg