Define stopping potential

When light of wavelength $\text{λ and 2λ}$ are incident on the metal surface, the stopping potentials are ${\mathrm{V}}_0 \mathrm{and} \frac{{\mathrm{V}}_0}{4}$ respectively. If $\mathrm{c}$ is the velocity of light in air, find the threshold frequency of the photoelectric emission.

Light rays of wavelength $\mathrm{\lambda } \mathrm{and} \frac{\mathrm{\lambda }}{2}$ are incident on a photosensitive metal. If the maximum kinetic energy of the emitted photoelectrons from the metal surface in the second case be $3$ times the maximum kinetic energy of emitted photoelectrons in the first case then determine the work function of the metal.