Answer
$\dfrac{8a^4}{b^6}$
Work Step by Step
RECALL:
(i) $\dfrac{a^m}{a^n} = a^{m-n}, a \ne 0$
(ii) $a^{-m} = \dfrac{1}{a^m}, a\ne0$
Divide the coefficients by each other and the variables by each other to obtain:
$=\dfrac{72}{9} \cdot a^{5-1} \cdot b^{11-17}
\\=8 \cdot a^{4} \cdot b^{-6}$
Use rule (ii) above to obtain:
$=8a^4 \cdot \dfrac{1}{b^6}
\\=\dfrac{8a^4}{b^6}$
