Using DATESBETWEEN and FILTER

Hi, 

I have two unrelated tables: 

• Fuel Purchases
• Days Worked

The Fuel Purchases table records the date a vehicle refuled as well as the date it was previously refuled.

The table Days Worked simply records the date a vehicle was on the road and wheather it worked that day or not. 

I'm looking to define a Measure on the Fuel Purchases table that will tell me the number of days that a particular vehicle worked between refueling dates (i.e. the number of days where 'Has the vehicle worked today?' = TRUE in the Days Worked table.)

Days Between Refuling= 
CALCULATE(
    COUNT('days_worked_table'[vehicle registration]), 
        DATESBETWEEN(
            'days_worked_table'[date],
            MIN('fuel_purchases'[previous_fuel_purchase_date]), 
            MIN('fuel_purchases'[fuel_purchase_date])
        )
)

But I'm clearly missing something to filter this by Vehicle Registration. 

Basically what' I'm trying to achieve is a Measure as per the column 'No. of days worked between refuling' in the example Fuel Purchases table above (highlighted in Yellow).