Answer
$-5a^2b^2+7ab^4$
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.
$=\dfrac{45a^3b^4}{-9ab^2} - \dfrac{63a^2b^6}{-9ab^2}
\\=-5a^{3-1}b^{4-2}+7a^{2-1}b^{6-2}
\\=-5a^2b^2+7ab^4$
