user: Question: What team was the away team when the home team scored 20.18 (138)?
Columns: ['Home team', 'Home team score', 'Away team', 'Away team score', 'Venue', 'Crowd', 'Date']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['Hawthorn', '20.18 (138)', 'South Melbourne', '15.16 (106)', 'Princes Park', 11657.0, '20 June 1981']
SQL:

assistant: SELECT "Away team" FROM "Table" WHERE "Home team score" = '20.18 (138)';