Currently, I am working on the Trailhead basics and having an issue with creating a new apex class after I deleted the same class in the dev console. 

DUPLICATE_VALUE
duplicate value found: <unknown> duplicates value on record with id: <unknown>




 

I am having issues with Creating  an Apex class that returns Account objects for the Mapping.net concepts challenge.  I am a VB and Javascript programmer and I can't seem to get the syntax right.   
public class AccountUtils {
    
    public static void accountsByState(String st){
       List<String> accts = [SELECT Id, Name FROM Account WHERE billingState = :st];
 }
  
}
I believe the first part is correct, but I cannot seem to get a return value.  I am confused by the constructors.  I have tried the documentation but I can't get a return value.  Please help.  I need to get this challenge complete.