DAX power pivot Average

I'd like to calculate the average for the total of sales for each month, per sale date not the total number of days per moth.

So in excel it would be

 SUM(F4:F11) /COUNT(E4:E11)

summed units / count of sales dates.

I've used

 Total Monthy:=VAR Mtotal = CALCULATE([Totalsales],ALL('Calendar'[Date]),VALUES('Calendar'[Month]) )
RETURN IF([Tsales],Mtotal)

To give me the total sales for each month but can't sum the number of dates for each month. I have tried various
AVERAGE, AVERAGEX option, but cant get the correct granularity,

I've attached a workbook with attempts and excel table with what I'd like to achieve.

Richard