Write SQL query to solve given problem: How many units are being sold for item 1 when the average temperature is 83?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(units) FROM weather AS T1 INNER JOIN sales_in_weather AS T2 ON T1.`date` = T2.`date` INNER JOIN relation AS T3 ON T2.store_nbr = T3.store_nbr WHERE T2.item_nbr = 1 AND T1.tavg = 83