Answer
$$2\times 10^{20}.$$
Work Step by Step
By raising each factor to the exponent and multiplying the double exponents, we have
$$
\frac{(50,000)(640,000,000)}{(0.0004)^2}=\frac{32,000,000,000,000}{0.00000016}\\
=2\times 10^{12+8}=2\times 10^{20}.
$$
which is in the scientific notation.
