user: Question: When  87 mpg-e (39kW-hrs/100mi) is the  epa rated combined fuel economy how many operating modes are there?
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)']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Mitsubishi i-MiEV', 'All-electric', 'mi (km)', '112 mpg-e (30kW-hrs/100mi)', '100 g/mi (62 g/km)', '200 g/mi (124 g/km)', '290 g/mi (180 g/km)']
SQL:

assistant: SELECT COUNT("Operating mode") FROM "Table" WHERE "EPA rated combined fuel economy" = '87 mpg-e (39kW-hrs/100mi)';