select c.cust_name,a.order_num, a.OrderTotal
from Customers c
join Orders o
on c.cust_id = o.cust_id
join
(
select order_num,sum(quantity*item_price) as OrderTotal
from OrderItems
group by order_num
)a
on o.order_num = a.order_num
order by c.cust_name,a.order_num