If the deBroglie wavelength of an electron is equal to $10^{-3}$ times the wavelength of a photon of frequency $6 \times 10^{14} \mathrm{~Hz}$, then the speed of electron is equal to : (Speed of light $=3 \times 10^8 \mathrm{~m} / \mathrm{s}$ Planck's constant $=6.63 \times 10^{-34} \mathrm{~J}-\mathrm{s}$ Mass of electron $=9.1 \times 10^{-31} \mathrm{~kg}$ )