Answer:
Length, l = 0.866 meters
Step-by-step explanation:
Given that,
Frequency of sound, f = 99 Hz
Speed of sound in air, v = 343 m/s
To find,
The length of a wind instrument.
Solution,
The standing wave will gets formed in wind instrument. For the closed tube, the closed tube the frequency is given by :

Where
l is the length of the instrument


l = 0.866 meters
So, the length of a wind instrument is 0.866 meters. Hence, this is the required solution.