Arrows arc motion

Hi guys

Im setting my tower defence game and I have some math problems.

I have a tower, that spawns projectiles, which is the arrow's shadow, so it moves on the ground. Now i want to attach the arrow sprite at the corresponding height.

Here is what i have:

<img src="https://dl.dropboxusercontent.com/u/19082408/ArrowArch.JPG" border="0" />

I have a local variable for the current height and i need it to show what height is suitable (the blue line)at every step of the way. I imagine lerp is the way but couldn't figure it out on my own. Any help is apreciated.

Thanks

Anyone?

Have a look at link which I think will help.

Yeah it looks like what i need

Hope i'll figure it out

Thanks RamPack