question: What was the number of US Viewers in the episode directed by Steve Shill and having a production code of E2102?
answer: SELECT us_viewers__millions_ FROM table_21781578_2 WHERE directed_by = "Steve Shill" AND production_code = "E2102"
context: CREATE TABLE table_21781578_2 (us_viewers__millions_ VARCHAR, directed_by VARCHAR, production_code VARCHAR)