A closed organ and an open organ tube filled by two different gases having same bulk modulus but different densities

A closed organ and an open organ tube filled by two different gases having same bulk modulus but different densities ρ1 and ρ2 respectively. The frequency of 9th harmonic of closed tube is identical with 4th harmonic of open tube. If the length of the closed tube is 10 cm and the density ratio of the gases is ρ1 : ρ2 = 1 : 16, then the length of the open tube is :

                                                                   (JEE-2025)