numerical

a) reflected light - Nothing changes in the reflected light.

b) Refracted light:The frequency of refracted light does not change.
      n = speed of light in air /speed of light in medium = wavelength of light in air/wavelength of light in medium

      1.33 = 3x10⁸ / speed in medium=>  speed in medium= 3x10⁸ / 1.33 = 2.20x10⁸ m/s

      1.33 = 589nm / wavelength in medium => wavelength in medium=589nm / 1.33 = 4.42nm