Answer
$2.1 \times 10^3$
Work Step by Step
Write each number in scientific notation to obtain:
$=\dfrac{8.4 \times 10^6}{4 \times 10^{3}}$
Divide 8.4 and 4 together and the powers of 10 together to obtain:
$=\dfrac{8.4}{4} \times \dfrac{10^6}{10^3}
\\=2.1 \times 10^{6-3}
\\=2.1 \times 10^3$
