Answer
$-7n^2+9$
Work Step by Step
Recall the following rule: $\frac{a^{m}}{a^{n}}=a^{m-n}$
In order to solve this problem, use the rule above and cancel out common factors that are in both the numerator and the denominator of the fraction.
$=\dfrac{-42n^6}{6n^4} + \dfrac{54n^4}{6n^4}
\\=-7n^{6-4} + 9n^{4-4}
\\=-7n^2+9n^0
\\=-7n^2+9(1)
\\=-7n^2+9$
