Question

[3/4 x(2-3/4)} x [3/5 x (4+ 1/2)]

Answer 1

Vamos por partes:
[3/4 x(2/1-3/4)] <- mmc de 1 e 4 = 4
[3/4 x(5/4)]
[15/16] 

[3/5 x (4+1/2)] <- mmc de 1 e 2 = 2
[3/5 x (9/2)]

15/16 x 27/10 = 405/160, que simplificados por 5 = 81/32