We know that the energy of a wave is given by:
E = nhc/λ; where n is the number of photons, h is the Planck's constant, c is the speed of light and λ is the wavelength. Substituting values:
0.363 = (n x 6.63 x 10⁻³⁴ x 3 x 10⁸)/(657 x 10⁻⁹)
n = 1.2 x 10¹⁸ photons
