Question

When two light beams of wavelengths 1and fall on a metal surface, they produce photoelectrons with energies 115 eV and 254 eV respectively. Estimate the numerical value of the Planck constant.

Answer 1

The Planck Constant is defined as the "proportionality between the energy carried by a photon and the frequency of its associated EM wave".
So, to estimate the Planck Constant, you should take the energies of the electrons and divide those values by their respective wavelengths; you should get approximately the same result from either division.