In medium A wavelength λA = 100 mm = 0.1 m
In medium A velocity vA = 80 m/s = 0.8 m/s
In medium B let velocity be vB
In medium B, wavelength λB = 0.25 m
As the frequency of the wave remains same in the two media, so
= 2 m/s
∴ Velocity of waves in the medium B = 2 m/s