1. [4 marks] Write a query to list a summary of customer balance for those customers who made purchase. More specifically, the summary should include the minimum balance, maximum balance, and average balance. 2. [4 marks] Write a query to list the most popular product's p_code, p_descript, vendor's name (v_name) and contact (v_contact). Product's popularity is defined by the total quantity that have already been sold [Hint: you can use view] 3. [4 marks] Write a PL/SQL anonymous block to list those customers' full name who has 0 balance. [Hint: use cursor] 4. [3 marks] Write a PL/SQL anonymous block to calculate the subtotal of an invoice. Initialize a scalar variable to a specified invoice. 1. [4 marks] Write a query to list a summary of customer balance for those customers who made purchase. More specifically, the summary should include the minimum balance, maximum balance, and average balance. 2. [4 marks] Write a query to list the most popular product's p_code, p_descript, vendor's name (v_name) and contact (v_contact). Product's popularity is defined by the total quantity that have already been sold [Hint: you can use view] 3. [4 marks] Write a PL/SQL anonymous block to list those customers' full name who has 0 balance. [Hint: use cursor] 4. [3 marks] Write a PL/SQL anonymous block to calculate the subtotal of an invoice. Initialize a scalar variable to a specified invoice