Answer
$$5.8\times 10^{-5}$$
Work Step by Step
In scientific notation, the number of significant digits is the number of digits in the leading number between $1$ and $10$. The final answer should have the same number of significant digits as the least number of significant digits in any of the numbers involved in the division:
$3.95\times 10^{4}$ has $3$ significant digits
$6.8\times 10^{8}$ has $3$ significant digits.
Therefore, the final answer should be rounded to have $2$ significant digits.
Rearrange factors and divide:
$$\frac{3.95\times 10^{4}}{6.8\times 10^{8}}=\bigg(\frac{3.95}{6.8}\bigg)\bigg(\frac{10^{4}}{10^{8}}\bigg)=5.8\times 10^{-5}.$$
