20) (a*)* (a*)** (a³) 2 = a4

20) $$\frac{(a^4)^3 \cdot (a^5)^2}{(a^{3})^{2n}} = a^4$$ $$\frac{a^{12} \cdot a^{10}}{a^{6n}} = a^4$$ $$\frac{a^{22}}{a^{6n}} = a^4$$ $$a^{22-6n} = a^4$$ Следовательно, $$22 - 6n = 4$$ $$-6n = 4 - 22$$ $$-6n = -18$$ $$6n = 18$$ $$n = 18 : 6$$ $$n = 3$$

Ответ: 3