look up field copy into account entity for plugin

hello,

 I will created 3 entities city,state,country  this entities contain default field except city[name* , new_State(fieldtype=lookup), new_country(fieldtype=lookup)]. Then i will create new custom field on account entity is  new_city,new_state,new_country. The main work is when i type in city field =jaypur then when i save the records in the state field=Rajsthan and in the country field=India will automatically written. what should i do , plz give me a related code for that problem

give me answer,

kiran_rajput