I searched it and all answers were wrong

What is the radius of a circle with an area of 78.5 cubic inches? use 3.14 for pie

Find solution of the linear equation y = 2/3x + 1/3

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?