Write SQL query to solve given problem: What was the dew point on the day the most units of item no.5 were sold in store no.3 in 2012?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT dewpoint FROM sales_in_weather AS T1 INNER JOIN relation AS T2 ON T1.store_nbr = T2.store_nbr INNER JOIN weather AS T3 ON T2.station_nbr = T3.station_nbr WHERE T2.store_nbr = 3 AND SUBSTR(T1.`date`, 1, 4) = '2012' AND T1.item_nbr = 5 ORDER BY units DESC LIMIT 1