BCE should be correct answer cause number+varchar in this case imspossible

A and D wrong cause they have invalid identifier "Discount". E wrong cause date can't multiple with number.

BCF is correct answer Please note: date+date is not allowed

It´s not a right decision plus a NUMBER with VARCHAR2 fields.

Seems like a sketchy question, have to assume surcharge contains only numerical characters in the string for F

BCF The three queries that use valid expressions are: B. SELECT product_id, (unit_price * 0.15 / (4.75 + 552.25)) FROM products; C. SELECT product_id, (expiry_date - delivery_date) * 2 FROM products; F. SELECT product_id, unit_price, unit_price + surcharge FROM products; Explanation: A. This query is invalid because the alias "S" is not defined anywhere in the query. B. This query is valid. It calculates a value based on the unit price of each product using a mathematical expression. C. This query is valid. It calculates the difference between the expiry date and delivery date for each product and multiplies it by 2. D. This query is invalid because the alias "discount" is not defined anywhere in the query. E. This query is invalid because you cannot multiply a date value by a number. F. This query is valid. It selects the product ID, unit price, and the sum of the unit price and surcharge for each product.

select '2'+3 from dual; it produces the SUM correctly so F is correct

B-C-F IS CORRECT IF the varchar-column has stored number.

why is D incorrect?

Is "-discount" in AD supposed to be an alias for the column?

IT is correct BCF because in the Datatype Varchar2 there may be a number. Oracle makes it an implicit cast and uses it as a number

you cant multiply date, BCF correct if varchar2 is number

bce should be