Higher the shell from where the electron is transitioning, higher will be the energy. So energy of K_β transition is more than K_α . Energy is inversely promotional to wavelength. So, λ (K_α) > λ (K_β) > λ (K_γ).
M_α is a transition of an electron from N shell to M shell and requires much less energy than K_α transition from L shell to K shell. Thus, in terms of wavelength, λ (M_α) > λ (L_α) > λ (K_α).