4. You land on Planet X and perform a simple experiment to study gravity on the planet's surface. So you pick up a rock and throw it straight up with initial velocity of v= 10 m/s (meters per second), from the height of 1 meter. You know that the height of the rock after t seconds is h(t) = 1 + 10t - 2/, where g is the acceleration due to gravity on the surface of Planet X. (a) (2 marks) At what time t will the rock come back down to the height of h(t) = 1 meter? (Your result will involve the unsepecified constant g.) (b) (2 marks) If the rock came back to the height of 1 meter after t = 12.5 seconds, what is the value of g on Planet X?