Setting a list Date field to it's date + 7 days using C#

I have a SharePoint list field called ArchiveDate.

In a C# function I'm looping through the list and have the item in question.

foreach (SPListItem fListItem in fList.Items)      
{       
   foreach (SPField field in fList.Fields)       
    {    

If fListItem[field.Id] has that column item with a date in it. How can I add 7 days to that date using C#?

i know I can set the value of the field to today as follows:

         DateTime dt = DateTime.Now;  
         tListItem["Archive Date"] = dt; 
         tListItem.Update();    

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