Решение:
a) $$(a^4)^5 \cdot a^3 = a^{4\cdot5} \cdot a^3 = a^{20} \cdot a^3 = a^{20+3} = a^{23}$$
б) $$(x^3y^7)^4 = x^{3\cdot4}y^{7\cdot4} = x^{12}y^{28}$$
в) $$(aa^6)^6 = (a^{1+6})^6 = (a^7)^6 = a^{7\cdot6} = a^{42}$$
г) $$(m^2)^6 \cdot (m^3)^8 = m^{2\cdot6} \cdot m^{3\cdot8} = m^{12} \cdot m^{24} = m^{12+24} = m^{36}$$