ASP.NET - linq to fetch index of string array

var _Col_Name_lst = (from DataColumn x in _hdr[0].Table.Columns
                      select x.ColumnName).ToArray();

_Col_Name_lst  ----- This has a collection of string array

like

0  - EMl

1  - AZEER

2 -  VISTA

--------

Here in above collection, i require array index of EMI or AZEER or VISTA whichever i pass to a linq.

so using linq on above collection --- "_Col_Name_lst "

i require index of any values EMI or AZEER or VISTA whichever i pass