showing total of PRICE using 3 tables PROBLEM URGENT??

I am using three tables for this, customer table, orders table and orderline table. When a user enters a orderid, the program should display the total order for a certain orderid. how can i use the SUM function in such a way that i can store the total order cost(price of orders) in a variable and display it in the ouput line function??

SET SERVEROUTPUT ON;
DECLARE
v_odNum NUMBER(8):= &sv_orderNum;
v_price NUMBER(7,2);
v_quantity NUMBER(5);

v_fname VARCHAR2(30);
v_lname VARCHAR2(30);
v_add VARCHAR2(30);

BEGIN
SELECT first, last, cadd, order_price, quantity, SUM(order_price * quantity) AS TOTAL
INTO v_fname, v_lname, v_add, v_price, v_quantity
FROM customer c, orders o, orderline ordl
WHERE c.custid = o.custid AND o.orderid = ordl.orderid
AND v_odNum = o.orderid

DBMS_OUTPUT.PUT_LINE('The total order for' ||v_odNum|| ' '|| 'is' || TOTAL);
END;
/

Code (markup):

If you like to see how the tables look tell me please.

 

SELECT first, last, cadd, order_price, quantity, SUM(order_price * quantity) AS TOTAL
INTO v_fname, v_lname, v_add, v_price, v_quantity, v_total
FROM customer c, orders o, orderline ordl
WHERE c.custid = o.custid AND o.orderid = ordl.orderid
AND v_odNum = o.orderid
group by first, last, cadd, order_price, quantity

 

Whatever column that is not in a function, you have to put them in the group by clause.