help with query

[Simon Cooper]

I need some help with a project for school, I have developed a database and trying to run a query that displays the revenue earned from a particular product. In my database I have the rates listed as day_rate, weekend_rate and week_rate I would like to list the revenue earned as one field in my query this is my SQL statement so far any help would be greatly appreciated.

SELECT tbl_customer.customer_name, tbl_equipment.`description`, tbl_loan.stock_no, tbl_loan.date_out, tbl_loan.date_returned
FROM tbl_customer, tbl_equipment, tbl_loan, tbl_stock
WHERE tbl_stock.equipment_id=tbl_equipment.equipment_id AND tbl_loan.stock_no=tbl_stock.stock_no AND tbl_loan.loan_id=tbl_loan.customer_id AND tbl_loan.customer_id=tbl_customer.customer_id