In an OBI reprt, how do I show a column that is +90 days from Actual Start Date?

Summary:

I have a column populated with Actual Start Date, and I need to show that date + 90 calendar days in a separate column

Content (required):

Actual Start Date

Version (include the version you are using, if applicable):

Taleo Enterprise: 21D.1.3

Code Snippet (add any code snippets that support your topic, if applicable):

Here's a bad guess....

CASE WHEN ("Submission Dates"."Offer Actual Start Date")  = 1 THEN TIMESTAMPADD+90 ELSE END.