How much money on average does Lucas Wyldbore spend on book orders?
average spend on book orders = AVG (price)
SELECT SUM(T1.price) / COUNT(*) FROM order_line AS T1 INNER JOIN cust_order AS T2 ON T2.order_id = T1.order_id INNER JOIN customer AS T3 ON T3.customer_id = T2.customer_id WHERE T3.first_name = 'Lucas' AND T3.last_name = 'Wyldbore'