A cylindrical casting is 0.4 m in diameter and 0.6 m in length. Another casting of the same metal is rectangular in cross-section, has a width-to-thickness ratio of 3, and has the same length and cross-sectional area as the cylindrical casting. Both pieces are cast under the same conditions. What is the ratio of the solidification times of the two castings? Use Chvorinov's rule and n=2.