SELECT us_national_average_electric_mix FROM table_24620684_2 WHERE dirty_electric_grid_rocky_mountains__denver_ = "380 g/mi (236 g/km)"
Ketika 380 g/mi (236 g/km) adalah Pegunungan Rocky Grid Dirty Electric (Denver) Berapa campuran listrik rata -rata nasional AS?
CREATE TABLE table_24620684_2 (us_national_average_electric_mix VARCHAR, dirty_electric_grid_rocky_mountains__denver_ VARCHAR)