A catapult throws a projectile at a castle but it lands 500

Question

A catapult throws a projectile at a castle, but it lands 5.00 m short of the castle wall. The position of the projectile as a function of time is given by the equation

r^→(t) =(21.7m/s)t i^ + [(12.5m/s)t - (4.90m/s²)t2]j^.

1) What is the average velocity of this projectile for the first 2.00 s of flight?

2) At what time is the y-component of the projectile's velocity zero?