a) $$\frac{3^{13} \cdot 27^2}{81^4} = \frac{3^{13} \cdot (3^3)^2}{(3^4)^4} = \frac{3^{13} \cdot 3^6}{3^{16}} = \frac{3^{13+6}}{3^{16}} = \frac{3^{19}}{3^{16}} = 3^{19-16} = 3^3 = 27$$
б) $$5 - 6x^2$$ при $$x = -\frac{1}{3}$$
$$5 - 6 \cdot \left(-\frac{1}{3}\right)^2 = 5 - 6 \cdot \frac{1}{9} = 5 - \frac{6}{9} = 5 - \frac{2}{3} = \frac{15}{3} - \frac{2}{3} = \frac{13}{3} = 4\frac{1}{3}$$
Ответ: a) 27; б) $$4\frac{1}{3}$$