Problem $4.(20$ points$)$ Photon Energy. $($a$)$ What voltage should be applied to accelerate an electron from zero velocity in order that it acquires the same energy as a photon of wavelength $0=0\mathrm{.}87$ m$?$ For $1$ nW of optical power, what is the averaged photon flux? $($b$)$ A photon of wavelength $1\mathrm{.}06$ m is combined with a photon of wavelength $10\mathrm{.}6$ m to create a photon whose energy is the sum of the energies of the two photons. What is the wavelength of the resultant photon?