This is simple if you have one line per report, but not so simple with two dimensions (report and line). You might get a simpler solution if your table was something like:
Report, Text1, Expression1, Text2, Expression2, ... Textn, Expressionn
Then, if you select a report, you can get the expression for each line using (say 3 for example)
Tip: best if your report selection list box is set to "one and only one" selection.
You may be able to use your structure by selecting both report and line (either from list boxes or through set analysis) and using
Hope that helps