CREATE TABLE table_name_81 (l_100km_combined INTEGER, mpg_uk_extra_urban VARCHAR, l_100km_urban__cold_ VARCHAR, mpg_uk_combined VARCHAR)
What's the average L/km combines when the L/100km Urban is 13.9, the mpg-UK combined is more than 28.5 and the mpg-UK extra urban is less than 38.7?
SELECT AVG(l_100km_combined) FROM table_name_81 WHERE l_100km_urban__cold_ = 13.9 AND mpg_uk_combined > 28.5 AND mpg_uk_extra_urban < 38.7