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