The velocity of the sound will be 329 meters per second at -2.3975 degree Celsius.
[tex]v=20 \sqrt{273+t} \\ \\
329=20 \sqrt{273+t} \\ \\
16.45 =\sqrt{273+t} \\ \\
270.6025=273+t \\ \\
t=-2.3975
[/tex]
This solution can also be seen from graph attached below. The blue horizontal line shows the velocity equal to 329 meter per second.
