21/2: 1 1/4+1 2/3*(-3/5)= 1/3*(-2/5): (-1/3)= -3 /12: (-2/5*1/3)=

2 1/2:1 1/4+1 2/3*(-3/5)=5/2:5/4-5/3×3/5=5/2×4/5-1=2-1=1
1/3*(-2/5):(-1/3)=-1/3×2/5:(-1/3)=-2/15:(-1/3)=2/15×3/1=2/5
-3 /12:(-2/5*1/3)=-3/12:(-2/15)=3/12×15/2=1/30