A) 3/4(1/2-4/5
3/4(1×5/2×5-4×2/5×2)
3/4(5/10-8/10)
3/4(5-8/10)
3/4(-3/10)
3/4×-3/10
3×-3/4×10
-9/40
B) 1/2×3/8+3/2×5/6
1×3/2×8+3×5/2×6
3/16+15/12
3×12/16×12+15×16/12×16
36/192+240/192
36+240/192/5-
276/192
276÷12/192÷12
23/16
C) 4/5-3/5/4
4/5-3/5×4
4/5-3×4/5
4/5-12/5
4-12/5
-8/10