What is the frequency of `9^(th)` overtone on a stretched of length and linear density 'm', when the tension is "T"?

In order to double the frequency of the fundamental note emitted by a streched string, the length is reduced to 3/4th of the original length and the tension is chaged. The factor by which the tension is to be changed is

A string 25 cm long and having a mass of 2.5g is under tension. A pipe closed at one end is 40 cm long. When the string is set vibrating in its firsy overtone and the air in the pipe in its fundamental frequency, 8 beats per sec are heard. It is observed that decreasing the tension in the string decreases the beat frequency. If the speed of sound in air is 320 m/s, find the tension in the string.

A closed organ pipe of length 'L' and an open organ pipe contain gases of densities rho(1) and rho_(2) respectively . The compressibility of gases are equal in both the pipes . If the frequencies of their first overtones are same then, the length of the open organ pipe is