What datastructure would you use to represent this format of data?

Answer 1

Not sure about LINQ:

But to represent them in Object Oriented fashion is straight-forward.

Agency -> n-Rules -> Each Rule has attributes

E.g.Rule Object will consist of:

class Rule { //Probably you would like to call something more business related
   String ruleName; //E.g. Duplicate Accounts at Same Agency
   int numberOfFlagged; //E.g 4
   int percent; //E.g. 1%
   int days; //E.g. 6
}

class Agency {
   List<Rule> rules;
}

Once you have the data loaded you represent in Excel or a View as you want.