Tính a 3/4+4/9.(-3/20) b (-1/3)^2022:(-1/3)^2019 .

Tính:

a) $\frac{3}{4} + \frac{4}{9} . (\frac{- 3}{20})$ ;

b) ${(\frac{- 1}{3})}^{2022} : {(\frac{- 1}{3})}^{2019}$ .