Format of my data doesn't allow me to filter

Hi forum,

I often need to export data from Primavera P6 to manipulate it in Excel.

If I export a column of codes such as 000-025 they look OK in the spreadsheet but when I try to do operations on the data such as using Autosum or filtering using Contains, it just doesn't work.
When I select a cell in this data, in the formula bar it looks like:

'000-025

I don't what this little mark to the left means or how to change my data to "normal" format so that I can use it?

Any ideas?

Thanks very much.

Dave