#### Answer

$3,949,000$ miles

#### Work Step by Step

We are given that there are $3.949\times10^{6}$ miles of highways, roads, and streets in the United States. Since the exponent is positive, move the decimal 6 places to the right.
Note that 6 places to the right will be 3 decimal places past the last digit (9), so we will add 3 zeroes after 9.
$3.949\times10^{6}=3,949,000$ miles