Table: fa_cup_match_2
Columns: tie_no
home_team
score
away_team
attendance

Question: What was the attendance for the game that has a tie number of 13?
SQL: SELECT SUM("attendance") FROM fa_cup_match_2 WHERE "tie_no" = '13'

Question: What is the average attendance when the Forest Green Rovers is the away team?
SQL: SELECT AVG("attendance") FROM fa_cup_match_2 WHERE "away_team" = 'forest green rovers'