Savannah is an astronaut, floating in space. Their rocket is powered by throwing rocks out of a hole in the back of the spaceship. The inertia of Savannah and their rocket together is 317 kg. Savannah also (in addition to the rocket and the person) has two 36 kg rocks on board. They are initially at rest. Savannah throws the first rock, and then they are moving with velocity 29 m/s. Then Savannah throws the second rock out of the back and they are moving with velocity 37 m/s .(b) With what velocity is the first rock Savannah threw moving through space