Table: congress_changes_11
Columns: district
vacator
reason_for_change
successor
date_successor_seated

Question: The successor for the Massachusetts 20th district was seated on what date?
SQL: SELECT "date_successor_seated" FROM congress_changes_11 WHERE "district" = 'Massachusetts 20th'

Question: Who vacated the Pennsylvania 6th district?
SQL: SELECT "vacator" FROM congress_changes_11 WHERE "district" = 'Pennsylvania 6th'