So it continues:
"You have already found v0 (the launch speed)." Does this mean that the v0 is -3.9 m/s?
vb= sqrt(vbx² + vby²)= sqrt(169 + 15.21)= 13.57 m/s
Is vb the final velocity of the ball?
As for the angle, I think that the relationship is tan(angle)= vby / vbx, which gives us an angle of -16.7°?