Calculate wavelength of emitted characteristic X-ray from a tungsten (Z=74) target when an electron drops from an M shell to a vacancy in K shell

Question

$(a)\;1.8 \times 10^{-12} m\qquad(b)\;1.8 \times 10^{-13} m\qquad(c)\;1.8 \times 10^{-11} m\qquad(d)\;1.8 \times 10^{-9} m$