5/12:1/4 - (-1/3)=5/12*4/1 - (-1/3)=5/3 + 1/3 = 6/3=2

(1/2)*(-4)-5 = -2-5=-7

4/9:(-2/3)+1=4/9*(-3/2)+1=-2/3+1=-2/3+3/3=1/3