Set Variable As Book Name

I am generating Excel reports (with different names) using VBA. The problem I'm having is that for a certain macro, it needs to create a new book, and then activate the original window. But because all the new reports have new names (but using same macros), the name written in code doesn't equal the book's new name. How can I set a variable to be the book name? I do know that the name of the original book will be equal to two letters plus the value in A7. The problem is this: I have written a macro that shows the following

Worksheets("Sheet2").Select
Workbooks.Add
Windows("FT Bi Test.xls").Activate

I need something more like this (though this exact code doesn't work):

Worksheets("Sheet2").Select
Workbooks.Add
Windows("FT " & Range("A7").Value ".xls").Activate

Or something like this:

Worksheets("Sheet2").Select
Workbooks.Add
Windows("FT " & Variable ".xls").Activate