If the formula is appearing in the viewable part of the text, it could be two things.
1. You have set the option to show formula's.
2. The field is formated as text.
To resolve option 1, just go into the excel option and uncheck the checkbox for the option. It's in the view tab.
To resolve option 2
1. Select the cell
2. Select Data....Text To columns in the excel menu.
3. When the wizard appears, just press finish.
4. Also format it as general in the cell format options, which should stop it from reverting to the incorrect format.