Measure using averages calculated individually

I have two data tables, one with manufacturing data and one with detailed scrap reasons. I wrote this measure to calculate the cost of scrap by multiplying the numbers of scrap per item code and the average cost of the parts also by item code, but I want it to average the part cost by item code since now it's averaging the cost of everything together if I use my slicer to pick multiple product codes (which may consist of multiple item numbers). How could I edit this so that it averages the part cost and multiplies it by the sum of rejects for each item number within a product code. I have an active relationship between the two tables for machine, and another for item #/PARTNO.