Arcing projectiles?

i’m making a turret defense game (the kind with one aimable turret) and one of the weapons will be a bomb. i think i know part of the formula for making it move in an arc, but i need to know the whole thing :). it has to start at the turret (duh) and the top of the arc has to be the mouse’s position when it was fired. if i use _xmouse as the y axis (by subtracting it from the _x) i think i should be able to use the simple y=mx+b equation. b would be the _y of the turret, x and y are obvious, and m would be somehow related to x to make y increase in an arc. not sure how to figure that part out. a simple link to somewhere that the formula is explained would be helpful, i’ve searched and can’t find it.