A spaceship is heading toward Planet X. While descending to the surface, its rockets produce 25 kN of upward thrust and the spaceship's speed decreases at a rate of 0.15 m/s^2 . Following the completion of its mission, the spaceship lifts off to return to its home planet. While leaving Planet X's surface, the rockets produce 75 kN of upward thrust and the spaceship's speed increases at a rate of 0.50 m/s^2. What is the mass of the spaceship and the acceleration due to gravity at the surface of Planet X? Assume that the acceleration due to gravity is constant.