Measure to Calculate the number of days between two date columns

[jb123]

I am trying to do something that is very easy in Excel but haven't found the correct syntax in Power BI yet. 

I need to create a measure that calcualtes the number of days between two dates.  I am not looking to do anything special like network days just plain old calendar days between dates in Column A to dates in Column B.  What is the simpliest way to calulate this in Power BI?

Thanks.

Judie