A. SELECT cust_first_name, cust_credit_limit * .05 AS DUE_AMOUNT
FROM customers
WHERE cust_incoms_level IS NOT NULL
AND due_amount IS NOT NULL;

B. SELECT cust_first_name, cust_credit_limit * .05 AS DUE_AMOUNT
FROM customers
WHERE cust_income_level != NULL
AND cust_credit_level !=NULL;

C. SELECT cust_first_name, cust_credit_limit * .05 AS DUE_AMOUNT
FROM customers
WHERE cust_income_level != NULL
AND due_amount !=NULL;

D. SELECT cust_first_name, cust_credit_limit * .05 AS DUE_AMOUNT
FROM customers
WHERE cust_income_level IS NOT NULL
AND cust_credit_limit IS NOT NULL;

E. SELECT cust_first_name, cust_credit_limit * .05 AS DUE_AMOUNT
FROM customers
WHERE cust_income_level <> NULL
AND due_amount <> NULL;