How to calculate average line in DAX which for SPC

[Porntas]

I want to calculate linear average line for Line graph (Average line of below picture is from fucntion)

I try to use DAX as CALCULATE(AVERAGEX(),ALLSELECTED()) but it not work I found problems

1. I linked Month Master[Month Name] With Test[Month] but the data is not show due to X-axis don't change as filter (From Month Master). But if I use Test[Month] as filter, it's my expectation. 

2. I want X-axis are BATCH ID but can filter by Month

3. It's will be a slot on line graph if there are blank cell in my query.

Please help me, I try for many days to solve

I've uploaded my file as below link
https://drive.google.com/file/d/1JL6Hyt3z3wtDqA1bmOLjWAn1IMN8-paR/view?usp=sharing