Please help me to solve it!

A 150 kg rocket is moving radially outward from the earth at an altitude of 150 km above the surface with a velocity of 3.6 km/sec. At this point, its final stage engine shuts off.

1) Ignoring any minor air resistance, what is the rocket’s velocity 790 km above the surface of the earth?”

2) Again ignoring any minor air resistance, what is the rocket’s velocity 790 km above the surface of the earth if its mass were 300 kg?

3) What is the maximum height of the rocket above the earth’s surface (using the initial rocket mass of $