time intelligence - Dax problem

Hi,

i have a dim Date table and i wish to create a total sum of production QTY for a selected period.

i want to take  a specifceic date and lookback 30 working days backward and sum up the productin QTY for this period.

for example:

the selected period :

if today is : 25.2.2020

minus 30 days :  26.1.2020 

 for every seleced days in this period i want it to calculate the sum QTY for 30 days before.

for example :

for the 27.1.2020

take the qty for every day (in the last 30 days) before this date (27.1.2020)

thanks in advance

ofir