How many subscribers have ended their trip at MLK Library and how many docks does that station have?
subscribers refers to subscription_type = 'subscribers'; ended their trip at refers to end_station_name; end_station_name = 'MLK Library'; number of docks a station have refers to dock_count;
SELECT COUNT(T1.id), T2.dock_count FROM trip AS T1 INNER JOIN station AS T2 ON T2.name = T1.start_station_name WHERE T1.end_station_name = 'MLK Library' AND T1.subscription_type = 'Subscriber' AND T2.dock_count = 19