Answer
a). $(1)$ increases
b). $+0.047m$
Work Step by Step
a). frequency = 256 Hz
When temperature increases, speed of sound increases but frequency is same.
Speed = wavelength X frequency
Speed increases, frequency is constant, so the wavelength of the sound wave will increase.
b). $v=331+0.6T$
When temperature increases by 20 degrees, change in speed of sound is:
$\Delta v=0.6\Delta T
=0.6(20)=12m/s$
Also, change in speed = change in wavelength X frequency
$12=change\,\, in\,\, wavelength \times 256$
Change in wavelength = +0.047m
