Table: tv_episode_data_90
Columns: no_by_series
no_by_season
title
directed_by
written_by
original_air_date
production_number
u_s_viewers_in_millions

Question: Name the number of series for 19
SQL: SELECT "no_by_series" FROM tv_episode_data_90 WHERE "no_by_season" = 19

Question: Name the viewers for 520
SQL: SELECT "u_s_viewers_in_millions" FROM tv_episode_data_90 WHERE "production_number" = 520