USERELATIONSHIP - What am I doing wrong?

I've become stuck using USERELATIONSHIP for the first time and I don't understand where I need to plug this into my Dax formula. 

I've watched several videos and read numerous posts and articles but still can't see what I'm doing wrong. I completely understand the concept of USERELATIONSHIP I just can't figure out the usage of it or where I'm going wrong. 

Here is my original formula (The inactive relationship is created and an active relationship already exists. )

% of Total (AA) =
DIVIDE( [Total AA],
CALCULATE( [Total AA],
ALL( 'tbl_aa'[AA (Cleaned)] ) ),
BLANK() )

Here are my attempts at plugging USERELATIONSHIP into the above, none of which work. 

% of Total (AA) =
DIVIDE( [Total AA],
CALCULATE( [Total AA],
ALL( 'tbl_aa'[AA (Cleaned)] ) ), USERELATIONSHIP('Calendar'[Date], tbl_mpl[last_closed_date])
BLANK() )

% of Total (AA) = 
DIVIDE( [Total AA], 
    CALCULATE( [Total AA], 
ALL( 'tbl_aa'[AA (Cleaned)] ) ), 
BLANK() 
USERELATIONSHIP('Calendar'[Date], tbl_mpl[last_closed_date]) )

% of Total (AA) = 
CALCULATE(
        DIVIDE( [Total AA], 
            CALCULATE( [Total AA], 
ALL( 'tbl_aa'[AA (Cleaned)] ) ), USERELATIONSHIP('Calendar'[Date], tbl_mpl[last_closed_date]) 
BLANK() )

I would appreciate some help with this