A.V. + ㄴ/은 지(가) . . . 되다 => "it's been . . . since . . ."

This pattern is used to indicate that a time period has lapsed since the action or event.

• 한국에 온 지(가) 10 년 됐어요.
  => It's been ten years since I came to Korea. 
• 밥 먹은 지(가) 3 시간 됐어요.
  => It's been three hours since I had my meal. 
• 친구를 만난 지 오래 됐어요.
  => It's been awhile since I saw my friend. 
• 고속도로가 생긴 지 얼마나 됐어요?
  => How long has it been since the highway was built?