What is the average price of the dishes on the menu "Zentral Theater Terrace"?
average price = AVG(price); Zentral Theater Terrace refers to menu;
SELECT SUM(T1.price) / COUNT(T1.price) FROM MenuItem AS T1 INNER JOIN MenuPage AS T2 ON T1.menu_page_id = T2.id INNER JOIN Menu AS T3 ON T2.menu_id = T3.id WHERE T3.name = 'Zentral Theater Terrace'