$${\left({\left(-\frac{2}{3}\right)}^{-3}+3·2^{-3}\right)}^{-2}$$

$$={\left({\left(-\frac{3}{2}\right)}^3+3·\frac{1}{2^3}\right)}^{-2}$$

$$={\left(-\frac{27}{8}+\frac{3}{1}·\frac{1}{8}\right)}^{-2}$$

$$={\left(-\frac{27}{8}+\frac{3}{8}\right)}^{-2}$$

$$={\left(-\frac{24}{8}\right)}^{-2}$$

$$={\left(-\frac{8}{24}\right)}^2$$

$$=\frac{64}{576}$$

$$=\frac{32}{288}$$

$$=\frac{16}{144}$$

$$=\frac{8}{72}$$