Ican't do these

you throw a rock off the top of a building located on the planet mars with an initial velocity of 10.0 m/s. the force of gravity on mars is ⅓ that of earth. it takes 12.0 s to hit the ground. how tall is the building?

you shot a gun straight up into the air with a velocity of 500 m/s. how long will it take before it hits the ground again?

you shoot a gun with a initial velocity of 500 m/s horizontally at the exact instant you drop a rock from exactly the same height (at 1.6 m off of the ground). which one will hit the ground first.