C# - Difference Between These LINQ Queries?

I use LINQ-SQL as my DAL, I then have a project called DB which acts as my BLL. Various applications then access the BLL to read / write data from the SQL Database.

I have these methods in my BLL for one particular table:

public IEnumerable<SystemSalesTaxList> Get_SystemSalesTaxList()
{
return from s in db.SystemSalesTaxLists
select s;
}
public SystemSalesTaxList Get_SystemSalesTaxList(string strSalesTaxID)
{
return Get_SystemSalesTaxList().Where(s => s.SalesTaxID == strSalesTaxID).FirstOrDefault();

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