Answer
$0.074$
Work Step by Step
If $k_{1}$ and $k_{2}$ are angular wavenumber in regions $1$ and $2$ respectively, the reflection coefficient takes the form
$R=\frac{|k_{1}-k_{2}|^{2}}{|k_{1}+k_{2}|^{2}}$
Here, $k_{1}=1.35\times 10^{11}$ $m^{-1}$
Here, $k_{2}=7.72\times 10^{10}$ $m^{-1}$
$\therefore$ $R=\frac{|1.35\times 10^{11}-7.72\times 10^{10}|^2}{|1.35\times 10^{11}+7.72\times 10^{10}|^2}$
or, $R\approx 0.074$
Therefore, the reflection coefficient is $0.074$
