A 4.00-kg model rocket is launched, expelling 57.0 g of burned fuel from its exhaust at a speed of 685 m/s. What is the velocity of the rocket after

A 4.00-kg model rocket is launched, expelling 57.0 g of burned fuel from its exhaust at a speed of 685 m/s. What is the velocity of the rocket after the fuel has burned? Hint: Ignore the external forces of gravity and air resistance.