Calculating the Time of a Bullet's Flight from a Rifle Aimed Horizontally

[spirit2014]

This is a four part problem, and I need help starting it. It states that a rifle is aimed horizontally at a target 30 m away, and the bullet hits the target 1.90 cm below the aiming point. How do I find the time of bullet's flight?

 

[Siracuse]

What do you understand about projectile motion?