Need ETA report based on items ordered and suppliers

I am trying to make a ETA report based on a list of orders to be filled and a list of items ordered from suppliers.
Below is a picture of both forms, left is orders to be filled and on the right form is items ordered with eta to fill orders on left form.
Capture1.PNG

I have been manually going through line by line and filling in the items eta, example below:

Capture2.PNG

I'm pretty good with formulas, but this is beyond me; I need to be able to do this formula driven because the lines I manually go through now are over 1300.