How many scenes are there on average in one act in Twelfth Night?
Twelfth Night refers to Title = 'Twelfth Night'; average scene = divide(sum(Scene), count(Act))
SELECT SUM(T2.Scene) / COUNT(T2.Act) FROM works AS T1 INNER JOIN chapters AS T2 ON T1.id = T2.work_id WHERE T1.Title = 'Twelfth Night'