Assignment:
You have a item that you bought but you lost the sales receipt. There are no price stickers on the item (one of those time saving features for stores) but you remember you gave the clerk $40 and received x in change. Given that the sales tax rate in you state is 6.65%, how would you go about figuring the cost of the item itself? You may have more than one unknown but create a formula for this relationship.
If you returned the item to a store in another state with a different tax rate, what would the tax rate need to be for you to get back more money that you paid out?
Provide complete and step by step solution for the question and show calculations and use formulas.