Caculating Future date

Question

Hi All,

I m developing a web page, in which i have a gridview, which is editable for admin.
In that grid view. there are multiple columns(Req_ID, Delivery_Date,Duration(in Days), Decommissioning_Date).
I want to calculate Decommissioning_Date as(Delivery_Date + Duration) at  run time in RowUpdating Event.
How to do this in c#?
Please Help..