Photons of energy 7 eV are incident on two metals A and B with work functions 6 eV and 3 eV respectively. The minimum de-Broglie wavelengths of the emitted photoelectrons with maximum energies are ${\mathrm{\lambda }}_{\mathrm{A}} \mathrm{and} {\mathrm{\lambda }}_{\mathrm{B}}$, respectively where $\frac{{\mathrm{\lambda }}_{\mathrm{A}}}{{\mathrm{\lambda }}_{\mathrm{B}}}$  is equal to __________.