Conditional formatting help

Hi,

I have a spreadsheet with a column for employee hours. Anything over 9 hours is considered overtime and we are tracking how many employees are working overtime on a daily basis so I conditionally formatted those cells with the following formula

=AND(B3>9)=TRUE

If a value over 9 is entered then the cell turns red indicating overtime.

Now my problem is, some employees may be working that day but for a different department so we would put N/A or whatever else in the cell instead of a number. When I do that the cell still turns red. Can someone please tell me how to fix this?