Missing comma/bracket in formula

Hi SF Community,

I am currently studying to become an admin, so fairly new to the formula's when creating reports. I am trying to get the days elapsed between today and a future date (when a customer is receiving their product - field in opportunity is called Car Delivery Date). Using this formula, I get the error message Syntax Missing ")".

This is the formula used:

CASE(WHEN ISBLANK(Opportunity.Car_Delivery_Date__c), NULL,

    FLOOR(Opportunity.Car_Delivery_Date__c - TODAY()))

I have read some answers to similar questions and it could be that there is a comma missing, not necessarily bracket. 

Can anyone advise me as to where I am going wrong ?

Thanks,

TJ