Mechanics (Physics) question PLEASE ANSWER!?

the HARP (High Altitude Research Project) gun can fire an 84.00 kg projectile containing scientific instrument staright up to an altitude of 179 km. If we pretend there is no air resistance , what muzzle spees is required to attain this altitude (m/s)? How long does the projectile remain at a height in excess of 100 km, the height of interest for high-altitude research (s)?