Answer
$600,000$ trees in New York City can clean $3\cdot 10^{8}mi$ of car traffic in a year.
Work Step by Step
$1$ tree$->500mi$
$600,000$ trees$->500\cdot 600,000mi$.
$ 500\cdot 600,000\qquad$... write as powers of $10$.
$=5\cdot 10^{2}\cdot 6\cdot 10^{5}\qquad$...apply The Product Rule $a^{m}\cdot a^{n}=a^{m+n}$ to solve $10^{2}\cdot 10^{5}$.
$=5\cdot 6\cdot 10^{2+5}\qquad$... simplify.
$=30\cdot 10^{7}\qquad$...write in scientific notation $N\cdot 10^{m},\ 1\leq N<10,\ N$ expressed in
decimal notation, and $m$ as an integer.
$=3\cdot 10\cdot 10^{7}\qquad$...apply The Product Rule again.
$=3\cdot 10^{1+7}$
$=3\cdot 10^{8}$