State the max temperature of the weather station which has the no.21 store on 2012/11/9.
no.21 store refers to store_nbr = 21; on 2012/11/9 refers to date = '2012-11-09'; max temperature refers to tmax
SELECT tmax FROM weather AS T1 INNER JOIN relation AS T2 ON T1.station_nbr = T2.station_nbr WHERE T2.store_nbr = 21 AND T1.`date` = '2012-11-09'