Answer
$$48.0\times 10^{-24} .$$
Work Step by Step
By adding the exponents and multiplying the like terms, we have
$$ (6\times 10^{-12} ) (20\times 10^{-9}) (400\times 10^{-6})\\
=(6) (20) (400) \times 10^{-12-9-6}\\
=48,000\times 10^{-27}=48.0 \times 10^{-24} .$$
