How to calculate average based on month selected from different Years

[MeeraD]

I have 2 table dates and Transactions

date table has data (all days and months)

Year	MOnth	date	ReportYear
2018	jan	01/01/2018	Previous year
2018	jan	02/01/2018	Previous year
2018	feb		Previous Year
2019	Jan		Current Year
2019	feb		Current Year

Now I have transaction Table

Year	Stream	Hour
2018	a	10
2018	a	20
2019	a	30
2019	a	40

Both the table are joined on Year column

Now i have 2 slicer 

• Month
• Report Year

and a table which shows

Stream	total Hours
a	Previous year hours = 30.  Selected months = Jan total hour= Monthly average  = 30/12 x 1 When multiple FYs is selected:  current Year hour= 30  Previous year = 70 Selected months = Jan 2018+Jan 2019+Feb 2019 = 3 months Total hours = (30/12) x 1 + (70/12) x 2