You can do it with three variables vx, vy, and t. t is the number of seconds you want it to take to hit the player and vx,vy are the horizontal and vertical velocities we will calculate from t. anyway the arrow launch will look like this:
create arrow at (enemy.x, enemy.y)
t = 1
vx = (player.X-enemy.X)/t
vy = (player.y-enemy.y)/t-arrow.Bullet.Gravity*t/2
arrow: bullet: set speed distance(0,0,xv,vy)
arrow: bullet: set angle of motion to angle(0,0,xv,vy)
dropbox.com/s/68mhi9hrwsjf7fl/bullet_proj_calc.capx