A knight sits on a castle wall during a siege.To while away the time, he notes that boulders catapulted from below land on the top of his wall with a vertical velocity of 5.7 m/s. If he is 45 m above the catapult, what is the initial velocity of the boulders? The acceleration of gravity is 9.8 m/s 2.

How do I find the answer if all I have is final velocity and accleration?