Answer:
The procedure in SQL is created as follows
Explanation:
--creating the procedure
CREATE OR REPLACE PROCEDURE prc_inv_amounts (W_IN IN NUMBER) 
AS 
--defining variables
W_CK NUMBER := 0; 
W_SUBT NUMBER := 0; 
W_TAX NUMBER := 0; 
BEGIN 
--Authentication process of the invoice
SELECT COUNT(*) INTO W_CK FROM INVOICE WHERE INV_NUMBER := W_IN; 
--Transaction confirmation 
IF W_CK = 1 THEN 
SELECT SUM(LINE_TOTAL) INTO W_SUBT FROM LINE 
WHERE 
--checking the invoice for the desired invoice number
LINE.INV_NUMBER = W_IN; 
W_TAX :=W_SUBT * 0.08; 
--updating the invoice
UPDATE INVOICE 
--setting the new values
SET INV_SUBTOTAL = W_SUBT, 
INV_TAX = W_TAX,
INV_TOTAL =W_SUBT + W_TAX 
WHERE INV_NUMBER = W_IN; 
--ending the if statement
END IF; 
--ending the procedure
END;