Slingshot, need Position/time, acceleration and velocity formulas

1. The problem statement, all variables and given/known data
What is the acceleration,position,and velocity formula for the launch of a slingshot.

2. Relevant equations

3. The attempt at a solution
I just dont know where to start tbh... I really need help i put this off and its due tommorrow....
If someone could respond i can give more information you just have to be willing to help.
One equation i saw was X(final)=X(initial)+V(initial i think)X t + 1/2 X a x t^2
Basically what me and my group (they arnt helping me) had to make some sort of water baloon launcher to hit our teacher 20m - 30m away, launching at 45 degrees.
We chose a Slingshot type of one, that's pretty ghetto but works.
Our launcher is 41 inchs high (1.04m) and what he wants us to do is for each of the three phases of the waterballoon (launch, flight, landing) he wants us to show the acceleration, position and velocity of each. All the while using Logger pro (program) to graph it.
logger pro is software that you put a video in mark a height that you know and plot points of the balloon which you can fit a certain line to the graph, quadratic in my case, and basically tell him the physics i used to find the acceleration, positionvs time and velocity of each phase...
I found the formula i want to use to figure out my Position but i dont know what to put for Acceleration and Velocity.

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