Projectile Motion: initial velocity problem

[msun5040]

Homework Statement

Determine the initial velocity of a projectile that reuturns to launch level 10.0 seconds after it is launched and lands 300.0m away from the launch site.

Homework Equations

Δx=v_0xt
Δy=v_0yt+1/2gt²

The Attempt at a Solution

[/B] 300=v_0x(10)
v_0x=30m/s
I don't know how to procees with this problem since it appears that I'm missing v_0y. I have time and the initial x component for velocity, but I don't know how I would use that to find the initial y component of velocity.

 

[CWatters]

The projectile (rather obviously) must take the same time to travel 300m horizontally as it does to travel vertically up and down.

So you know the time it takes to get to the top of the flight. You also know the acceleration and the final velocity at the top. Find an equation that gives you the initial vertical velocity.