Hello, this is a question from the chapter "Sequence and series". Please help (also give explanation for each of them if possible)

6n^2-7n-75=0 solve by quadratic formula

How do businesses a country's economy? a. by investing in goods and services b. by increasing the unemployment rate c. by making profits

Clarence wants to buy a new car. he finds an ad for a car that costs 27,200 dollars. suppose his local sales tax is 7%. -how much would he have to pay? -what is the cost of the car including tax? -if clarence has 29,864 saved, can he pay cash to buy the car?