26.5 m/s
Ignoring air resistance, the projectile will have an initial kinetic energy expressed by
E = 0.5 M V^2
and as the projectile travels upward, it's kinetic energy will decrease while it's potential gravitational kinetic energy increases such that the sum of both is constant. Then once it starts to descent, the potential energy is converted back into kinetic energy. And when it finally reaches the ground, it's kinetic energy will exactly match the original kinetic energy it had initially. And the only way it can match since the mass never changes is for it to have the same velocity as it had when it was first fired.
