I have to solve this exercise, but I'm just starting with SQL.
I did the following:
1)SELECT product_id, product_name FROM Products
2)SELECT Orders.order_id, Products.product_id, Products.product_name, Order_Items.quantity FROM Orders, Products, Order_Items
3) INSERT INTO Orders VALUES customer_name FROM Customers
For the solution of the second question you should do something like this.
and for the third:
I hope it helps you