A grain silo consists of a cylindrical concrete tower surmounted by a metal hemispherical dome. The metal in the dome costs 1.8 times as much as the concrete (per unit of surface area). If the volume of the silo is 600 m, what are the dimensions of the silo (radius and height of the cylindrical tower) that minimize the cost of the materials? Assume the silo has no floor and no flat ceiling under the dome. The radius of the cylindrical base (and of the hemispherical dome) is (Round to the nearest tenth as needed.)