Karia,

Try this:
=INDIRECT(A1&"!B7")
This will give you the contents of cell B7 of the sheet mentioned in
cell A1 of the current sheet.
So if A1 is FLX_79, you get the same result as when you write =FLX_79!
B7
Or instead of entering the name in a cell, you could create a defined
name (Insert/Name/Define) like
="FLX_79" and name this 'Detail1' then your formula would be
=INDIRECT(Detail1&"!B7")

DQ