It seems that the due date was in April, are you just trying to solve it for your own fun? In this case I would recommend starting with something a bit simpler until you become more familiar with LabVIEW.
I certainly don't want to complete the assignment for you. You are currently struggling with a simple dataflow issue: The "average weight array" will get data once the while loop finishes, e.g. after you press the stop button. (try it!).