Slanted throw with spring cannons?

Hello, hello, hello. We don't have much time today, so I'll start right away:

A small ball with a mass of m = 4 g is fired from a spring cannon at an elevation angle of α = 30 ◦. At the beginning of the acceleration phase, the spring is compressed with a spring constant of D = 2.0 Ncm−1 by a length of l = 1.5 cm (position 1). When the ball leaves the spring cannon (position 2), the spring is just relaxed.

a) Calculate the velocity v0 (measured in m/s) of the ball as it leaves the spring cannon (position 2). Consider the difference in height of the ball between positions 1 and 2, where g = 9.81 m/s 2 .

(b) What height hs (measured in cm) does the ball's center reach at the apex of the trajectory (position 3)? Upon leaving the spring gun, the center has a height of h0 = 2.5 cm.

c) Calculate the velocity vs (measured in m/s) of the ball at the apex of the trajectory.

Jensek81 approach

a) Epot = 1/2 k x²
Epot = 1*2 * 20 N/cm^-1 )1.5 cm)² = 2.25 NCm

vo = √(o.225 Nm/ 0.0004 kg) = 7.6 m/s

b) E kin = Epot
1/2 v² = mgh

=> h = vo² / 2 g = 7.5m² / 2 * 9.81 = 2.87 m
c) Epot = Ekin
=> vs = √2gh = √2*9.81 *2.87 = 7.52 m

Best regards,
Lars-Aaron Böhmkutter