Telephone signals are often transmitted over long distances by microwaves. what is the frequency of microwave iradiation with a wavelength of 3.50 cm

c = speed of light = 3.00 x 10^5 km/s = 3.00 x 10^8 m/s
  λ = wavelength of the microwave radiation = 3.50 cm = 0.035 m
  f = frequency (in Hertz) = to be determined
    f = c/λ = 3.00 x 10^8 m/s / 0.035 m
  f = 8.57 x 10^9 Hz Frequency