Answer
$2.22\times 10^{10}$
Work Step by Step
As the e reflection coefficient $R=0.074$, we can say that an electron has $0.074\%$ chance of being reflected.
The incident beam sends $3.00\times10^9$ electrons against
the potential step.
Therefore, the number of electrons will be reflected is
$=3.00\times10^9\times \frac{0.074}{100}\times100$
$=2.22\times 10^{10}$
