This is known as a compound index.
Open the table in design mode. Open the index dialog.
In the "Index Name" column, enter your name for the index
In the "Field Name" column, select EstItem
In the "Sort Order" columns, select Ascending or Descending
On the next line of the index grid, leave the "Index Name" column blank
In Field Name, select LineNo, then select Asc. or Desc.
-TedMi