Question: What is the dirty electric grid rocky mountains (denver) for the vehicle with the clean electric grid california (san francisco) of 160 g/mi (99 g/km)?
Schema: create table table_23840623_4 (dirty_electric_grid_rocky_mountains__denver_ varchar, clean_electric_grid_california__san_francisco_ varchar, PRIMARY KEY (dirty_electric_grid_rocky_mountains__denver_))
SQL: select dirty_electric_grid_rocky_mountains__denver_ from table_23840623_4 where clean_electric_grid_california__san_francisco_ = "160 g/mi (99 g/km)"