Tell the wet-bulb temperature of the weather station which contained store no.6 on 2012/2/15.
store no.6 refers to store_nbr = 6; on 2012/2/15 refers to date = '2012-02-15'; wet-bulb temperature refers to wetbulb
SELECT T1.wetbulb FROM weather AS T1 INNER JOIN relation AS T2 ON T1.station_nbr = T2.station_nbr WHERE T2.store_nbr = 14 AND T1.`date` = '2012-02-15'