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What situation is an example of an observational study

Ifurniture stores having a weekend sale and is offering 20% discount on patio chairs and table the sales tax on furniture is 6.25 using function composition how can you represent the total amount a that you would need to pay for this furniture that cost x dollars

Asporting good store is offering 30 percent off of the original price(x) of football cleats. the discount will be reduced by an another $7 before sales tax.