To add or subtract terms with exponents, both the base and the exponent must be the same. In this case they are so subtract the coefficients and retain the base and exponent:

-7x³ - 1x³
(-7 - 1)x³
-8x³

To subtract these radicals together their radicands must be the same:

3\( \sqrt{28} \) - 9\( \sqrt{7} \)
3\( \sqrt{4 \times 7} \) - 9\( \sqrt{7} \)
3\( \sqrt{2^2 \times 7} \) - 9\( \sqrt{7} \)
(3)(2)\( \sqrt{7} \) - 9\( \sqrt{7} \)
6\( \sqrt{7} \) - 9\( \sqrt{7} \)

Now that the radicands are identical, you can subtract them:

To raise a term with an exponent to another exponent, retain the base and multiply the exponents:

To divide terms with exponents, the base of both exponents must be the same. In this case they are so divide the coefficients and subtract the exponents:

\( \frac{x^6}{6x^3} \)
\( \frac{1}{6} \) x^{(6 - 3)}
\(\frac{1}{6}\)x³

Average speed in miles per hour is the number of miles traveled divided by the number of hours:

Solving for time:

time = \( \frac{\text{distance}}{\text{speed}} \)
time = \( \frac{390mi}{65mph} \)
6 hours