In the X-ray spectrum of niobium (Z = 41), a Ka peak is observed at a wavelength

Question:

In the X-ray spectrum of niobium (Z = 41), a Ka peak is observed at a wavelength of 7.462 x 10-11 m.
(a) Determine the magnitude of the difference between the observed wavelength of the Ka X-ray for niobium and that predicted by the Bohr model.
(b) Express the magnitude of this difference as a percentage of the observed wavelength.