A string of length `50 cm` and mass `12.5 g` is fixed at both ends. A pipe closed at one end has a length `85 cm`. When the string vibrates in its second overtone and the air column in the pipe in its first. Overtone, they produce a beats frquency of `6 Hz`. It is also observed that decreasing teh tension in the string decreaes beats frequency. Neglect the end correction in the pipe and velocity of sound in air is `340 m//s`. then the tension in the string is