2.7GHz f = c / λ - λ = 11E-2m and c = 3E8m/s
freq = c/wavelength = 1.58 x 10^9 1.58 GHz.
frequency = (3x10^8 m/s)/(0.19 m) = 1.6 x 10^9 Hz.
Any one of these answers may be correct as it depends on many different factors which are not included in your rather silly question.
Well it is as sill as asking
"What is the best time to eat bananas"................. Oh! and the answer to that is:
"While you are still up in your tree"