<span>A wave with a large amplitude has a lot of a.vibration b.speed <u> c.energy</u></span>

Actually Welcome to the Concept of the Projectile Motion.
Since, here given that, vertical velocity= 50m/s
we know that u*sin(theta) = vertical velocity
so the time taken to reach the maximum height or the time of Ascent is equal to
T = Usin(theta) ÷ g, here g = 9.8 m/s^2
so we get as,
T = 50/9.8
T = 5.10 seconds
thus the time taken to reach max height is 5.10 seconds.
B. Elastic potential to kinetic energy
The elastic potential energy in the slingshot will be transferred to the stone as kinetic energy as the stone is launched.