Date manipulation in expression-based columns

Question

I want to create an expression-based column in DataSet that can do some manipulation on another DateTime column. Specifically, I have a database column named DateEnrolled. I want to create a column called ExpectedGraduationDate, which is equal to DateEnrolled + 180 (days).

I have tried to put in the Expression property of the ExpectedGraduationDate the following:
1. DateEnrolled + 180 // did not work
2. DateEnrolled.Add(180) // did not work either

Does ADO.NET expression-based columns support SQL date manipulation functions? Is there any way to work around that issue?