# its physics.. i just want the formula

posted by
**Rah_rAh**
.

A boy on a 2.2 kg skateboard initially at rest

tosses a(n) 7.7 kg jug of water in the forward

direction.

If the jug has a speed of 2.9 m/s relative to

the ground and the boy and skateboard move

in the opposite direction at 0.57 m/s, find the

boy’s mass.

Answer in units of kg

(I just want the formula) due in about 2 hours