List all representatives of districts which have more than 30 000 population in 2020.
more than 30000 population in 2020 refers to population_2020 > 30000; representative refers to first_name, last_name
SELECT T3.first_name, T3.last_name FROM zip_data AS T1 INNER JOIN zip_congress AS T2 ON T1.zip_code = T2.zip_code INNER JOIN congress AS T3 ON T2.district = T3.cognress_rep_id WHERE T1.population_2020 > 30000 GROUP BY T3.first_name, T3.last_name