Resposta:

a) 80; b) 193/360; c) 44/9.

Explicação passo a passo:

a) 2/3 de 120 =

120 : 3 x 2 =

40 x 2 =

80.

b) 5/6 + 1/8 - ( 2/9 + 1/5 ) =

Igualando os denominadores:

5/6 + 1/8 - (10/45 + 9/45) =

20/24 + 3/24 - 19/45 =

23/24 - 19/45 =

345/360 - 152/360 =

193/360.

c) [(2/5 + 1/3): ( 1/5)] : (3/4) =​

Igualando os denominadores:

[(6/15 + 5/15) : 1/5] : 3/4 =

[11/15 : 1/5] : 3/4 =

[11/15 x 5/1] : 3/4 =

55/15 x 4/3 =

220/45 = 44/9.