а) $$4\frac{1}{6}a^8b^5 \cdot \left(-1\frac{1}{5}a^5b\right)^3 = \frac{25}{6}a^8b^5 \cdot \left(-\frac{6}{5}a^5b\right)^3 = \frac{25}{6}a^8b^5 \cdot \left(-\frac{6^3}{5^3}a^{15}b^3\right) = \frac{25}{6} \cdot \left(-\frac{216}{125}\right) \cdot a^8 \cdot a^{15} \cdot b^5 \cdot b^3 = -\frac{25 \cdot 216}{6 \cdot 125}a^{23}b^8 = -\frac{5 \cdot 36}{1 \cdot 25}a^{23}b^8 = -\frac{180}{25}a^{23}b^8= -\frac{36}{5}a^{23}b^8 = -7\frac{1}{5}a^{23}b^8$$.
Ответ: $$-7\frac{1}{5}a^{23}b^8$$
б) $$a^{m+1} \cdot a \cdot a^{3-m} = a^{m+1+1+3-m} = a^{m-m+5} = a^5$$.
Ответ: $$a^5$$