How many of these occur at least 200 times?
SELECT count ( DISTINCT start_station_id )  FROM trip WHERE start_station_id IN  ( SELECT start_station_id FROM trip GROUP BY start_station_name HAVING COUNT ( * )   > =   200 ) 
occur at least 200 times refers to HAVING COUNT(*) >= 200; counting distinct occurrences refers to COUNT(DISTINCT column_name);