A cylinder has a surface area of 339cm. The radius is two times greater than the height. what is the radius of the cylinder.

The answer is 6 cm.

The surface area of the cylinder is:

SA = 2πr² + 2πrh

SA = 339

r = 2h

⇒ h = r/2

r = ?

π = 3.14

339 = 2πr² + 2πr*r/2

339 = 2πr² + πr*r

339 = 3πr²

πr² = 339/3

πr² = 113

r² = 113/π

r² = 113/3.14

r² ≈ 36

r = √36

r = 6