## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$6.51\times10^{3}$
Using the laws of exponents and the concepts of scientific notation, the given expression, $(3.1\times10^7)(2.1\times10^{-4})$, simplifies to \begin{array}{l} (3.1)(2.1)\times10^{7+(-4)} \\\\= 6.51\times10^{3} .\end{array}