1 + 1 = 3 is this right

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

Jenisey has $24 to spend on seven pencils. after buying them she had $10. how much did each pencil cost.?