The figure shows an iron ball suspended by thread of negligible mass from an upright cylinder that floats partially submerged in water. The cylinder has a height of 6.90 cm, a face area of 13.0 cm2 on the top and bottom, and a density of 0.304 g/cm3, and 1.70 cm of its height is above the water surface. The water has a density of 1000 kg/m3, and the iron has a density of 7900 kg/m3. What is the radius r of the iron ball?