a) $$b^{12} \cdot b^{11} = b^{12+11} = b^{23}$$
б) $$y^{20} : y^{14} = y^{20-14} = y^6$$
в) $$(x^7)^3 = x^{7 \cdot 3} = x^{21}$$
г) $$(ay)^6 = a^6y^6$$
д) $$(\frac{c}{5})^4 = \frac{c^4}{5^4} = \frac{c^4}{625}$$
Ответ: а) $$b^{23}$$, б) $$y^6$$, в) $$x^{21}$$, г) $$a^6y^6$$, д) $$\frac{c^4}{625}$$