First, convert the wavelength into SI units: λ = 4.00 cm = 0.04 m. Now compute the momentum:$p = \;\frac{6.63 \times 10^{-34}}{0.04}$$p = 1.6575 \times 10^{-32}\,\text{kg}\,\text{ms}^{-1}$Rounding to appropriate significant figures gives $1.66 \times 10^{-32}\,\text{kg}\,\text{ms}^{-1}$The momentum of the photon is $1.66 \times 10^{-32}\,\text{kg}\,\text{ms}^{-1}$.