Planck’s Quantum Theory

If the energies of two light radiations $E_1$ and $E_2$ are $25\mathrm{eV}$ and $100\mathrm{eV}$ respectively, then their respective wavelengths ${\lambda }_1$ and ${\lambda }_2$ would be in the ratio ${\lambda }_1:{\lambda }_2=$

If the work function for the photoelectron emission of a metal is $3.75\mathrm{eV}$, then the threshold wave length of the radiation needed for the ejection of the electron is approximately