Answer:
f = 1.354*10^{20} Hz
Step-by-step explanation:
By conservation of linear momentum, wavelength shift due to collision of photon to electron is given by following formula

where h is plank constant = 6.626*10^{-34}
c = speed of light = 3*10^{8} m/s
scattered angle = 60 degree
m = rest mass of electron = 9*10^{-31}


we know that 1 pm = 10^{-12}m


f = 1.354*10^{20} Hz