<p><strong>а)</strong> $$4a^{4}b^{-6} \cdot 3a^{2}b^{3} = 4 \cdot 3 \cdot a^{4+2} \cdot b^{-6+3} = 12a^{6}b^{-3} = \frac{12a^{6}}{b^{3}}$$</p>
<p><strong>б)</strong> $$\frac{x^{4}y^{-6}}{x^{-1}y^{-7}} = x^{4-(-1)} \cdot y^{-6-(-7)} = x^{5} \cdot y^{1} = x^{5}y$$</p>