I have 5 possible values (chosen from a dropdown) that can be entered in cells B19-B21: 

> 
> N/A, NOT STARTED, IN PROCESS, OVERDUE, COMPLETE
> 
> 
> 

The condition I want to write for the header row B18 would say in plain English:

If B19-B21 all = some combination of "COMPLETE" or "N/A" then B18= "COMPLETE"; Else = "INCOMPLETE"

I have read several similar discussions on conditional formatting but am having trouble finding where to start with the above scenario. Any help is greatly appreciated!