CREATE TABLE table_27012 ("Vehicle" TEXT, "Operating mode" TEXT, "EPA rated All-electric range" TEXT, "EPA rated combined fuel economy" TEXT, "Clean electric grid California  ( San Francisco ) " TEXT, "U.S. national average electric mix" TEXT, "Dirty electric grid Rocky Mountains  ( Denver ) " TEXT)

When 380 g/mi (236 g/km) is the dirty electric grid rocky mountains (denver) what is the u.s national average electric mix?
SELECT "U.S. national average electric mix" FROM table_27012 WHERE "Dirty electric grid Rocky Mountains (Denver)" = '380 g/mi (236 g/km)'
SELECT "U.S. national average electric mix" FROM "table_27012" WHERE "Dirty electric grid Rocky Mountains (Denver)" = '380 g/mi (236 g/km)'