Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
When 380 g/mi (236 g/km) is the dirty electric grid rocky mountains (denver) what is the u.s national average electric mix?

### Inputs:
table_name: table, columns: ['Vehicle', 'Operating mode', 'EPA rated All-electric range', 'EPA rated combined fuel economy', 'Clean electric grid California (San Francisco)', 'U.S. national average electric mix', 'Dirty electric grid Rocky Mountains (Denver)']

### Response:
SELECT U.S. national average electric mix FROM table WHERE Dirty electric grid Rocky Mountains (Denver) = 380 g/mi (236 g/km)