Energy #E# of one photon
#E=h nu# .....(1)
here #h# is Planck's constant and #nu# frequency of photon
Wave equation is
#c=nulambda .....(2)#
where #c# is velocity of light in vacuum and #lambda# is the wavelength of light.
Combining two equations we get
#E=hxxc/lambda#
if number of photons emitted is #n#, total energy emitted is
#E_"Total"=nhc/lambda=31.0#
#=>n=(31.0xxlambda)/(hc)#
Inserting various values, #h=6.6261 × 10^-34 m^2 kg s^-1 ,c=3xx10^8ms^-1# we get
#n=(31.0xx(785xx10^-9))/((6.6261 × 10^-34)xx(3xx10^8))#
#=>n=1.224xx10^20#, rounded to three decimal places.
