SSAS MDX sum only selected members in time dimension

i have a cube, that need to create a calculate measure that sum only the numbers of days in selected month.  I need this because i have a formula that is like A * Number of days in a month / total days of month selected

I resolve this with dynamics named sets but, Power BI doesnt support it.  Then need to resolve this without using named sets

For example:

Month         number days        Total selected

Q1               59                           59

January        31                           59

February      28                            59

Any know or have an idea how to resolve with MDX in a SSAS MD?

Thanks for any help or idea

Juan 

Juan Alvarado - MVP SQL SERVER