You can use an expression like:
=Sum(IIf(Fields!ValueFor.Value = "Total Contacts", Fields!MyValue.Value, Nothing))
/ Sum(IIf(Fields!ValueFor.Value = "Abandons", Fields!MyValue.Value, Nothing))
Using a conditional Sum
as above you can look at all records in a particular Scope but only consider the ones that fulfill that particular criterion - by combining two you can get your required result.
Edit after comment
With your data:
I have a simple table:
Note that the expressions are all in the table footer row.
The expressions are:
FirstHr
=Sum(IIf(Fields!ValueFor.Value = "Total Contacts", Fields!FirstHr.Value, Nothing))
/ Sum(IIf(Fields!ValueFor.Value = "Abandons", Fields!FirstHr.Value, Nothing))
SecondHr
=Sum(IIf(Fields!ValueFor.Value = "Total Contacts", Fields!SecondHr.Value, Nothing))
/ Sum(IIf(Fields!ValueFor.Value = "Abandons", Fields!SecondHr.Value, Nothing))
ThirdHr
=Sum(IIf(Fields!ValueFor.Value = "Total Contacts", Fields!ThirdHr.Value, Nothing))
/ Sum(IIf(Fields!ValueFor.Value = "Abandons", Fields!ThirdHr.Value, Nothing))
Works fine for that dataset: