Table: challenger_clients
Columns: client
years_of_operation
area_of_operation
country
services

Question: Whose address of operation was the Echirax Concession? 
SQL: SELECT "client" FROM challenger_clients WHERE "area_of_operation" = 'EchiraX Concession'

Question: When was the operation in Field 103 executed? 
SQL: SELECT "years_of_operation" FROM challenger_clients WHERE "area_of_operation" = 'Field 103'

Question: In what country is the El Hamada area of operation? 
SQL: SELECT "country" FROM challenger_clients WHERE "area_of_operation" = 'El Hamada'