Answer:
The fifth harmonic frequency is 2.9 KHz.
Step-by-step explanation:
For a closed tube, the fifth harmonic frequency is also the second overtone. So that;
fifth harmonic frequency =

where V is the velocity of the sound in air, and L is the length of the tube.
But L = 0.15 m and V = 343 m/s, then:
fifth harmonic frequency =

=

= 2858.33 Hertz
fifth harmonic frequency = 2.9 KHz
The fifth harmonic frequency of the soda bottle is approximately 2.9 KHz.