a)  ${\left(\frac{1}{5}+\frac{2}{3}+\frac{4}{5}+\frac{1}{3}-2\right)}^3={\left(\frac{4}{5}+\frac{1}{5}+\frac{2}{3}+\frac{1}{3}-2\right)}^3={\left(\frac{5}{5}+\frac{3}{3}-2\right)}^3={\left(1+1-2\right)}^3={\left(2-2\right)}^3=0^3=0$

b)  $\frac{4}{5}+\frac{3}{4}+\frac{2}{3}+{\left(\frac{1}{3}\right)}^2+{\left(\frac{1}{4}+\frac{1}{5}\right)}^2=\frac{16}{20}+\frac{15}{20}$