Answer
$$6.25 \times 10^{-18}
.$$
Work Step by Step
We simplify by raising each factor to the exponent and then by division we have
$$
\frac{(5 \times 10^{-6})^2}{4 \times 10^{6}}=\frac{25 \times 10^{-12}}{4 \times 10^{6}}=6.25 \times 10^{-18}
.$$
