Answer
$\dfrac{3b^7}{a^6c^8}$
Work Step by Step
RECALL:
(i) $a^m \cdot a^n = a^{m+n}$
(ii) $a^{-m} = \dfrac{1}{a^m}, a\ne0$
(iii) $a^0=1, a\ne0$
Use the rules above to have:
$=\dfrac{12}{4} \cdot a^{-1-5}b^{6-(-1)}c^{-3-5}
\\=3 \cdot a^{-6}b^{6+1}c^{-8}
\\=3 \cdot \dfrac{1}{a^6} \cdot b^7 \cdot \dfrac{1}{c^8}
\\=\dfrac{3b^7}{a^6c^8}$
