I'm having a hard time with this one solve for y 3y+7=28?

Answer these questions showing your work plz

Use the quadratic function to predict f(x) if x equals 8. f(x) = 25x2 − 28x + 585

You just purchased two coins at a price of $670 each. because one of the coins is more collectible, you believe that its value will increase at a rate of 7.1 percent per year, while you believe the second coin will only increase at 6.5 percent per year. if you are correct, how much more will the first coin be worth in 15 years?