For C#:
DateTime d1=DateTime.MinValue;
DateTime d2=DateTime.MaxValue;
TimeSpan span=d2-d1;
For SQL;
The basic interpretation for your third column would be as follows (the "d" tag measures the date difference in days):
DateDiff("d",[DateReceived],[DateClosed])
If you want to add an exception that handles records with no closed date, use this one (optionally, if you just want to look at records where there is a closed date, add "Is Not Null" as the criteria for ClosedDate and use the top expression):
IIf(IsNull([DateClosed]),"Not Closed Message",DateDiff("d",[DateReceived],[DateClosed]))
Good luck,
OI