A=7/6+5/4-13/12
A = 7 x 4 / 6 x 4 + 5 x 6 / 4 x 6 - 13 x 2 / 12 x 2
A = 28/24 + 30/24 - 26/24
A = 32/24
A = 8 x 4 / 8 x 3
A = 4/3
B=5/11-2/3+1/2
B = 5 x 6 / 11 x 6 - 2 x 22 / 3 x 22 + 1 x 33 / 2 x 33
B = 30/66 - 22/66 + 33/66
B = 41/66
C=1/3-4/8-5/6
C = 1 x 8 / 3 x 8 - 4 x 3 / 8 x 3 - 5 x 4 / 6 x 4
C = 8/24 - 12/24 - 20/24
C = 24/24
C = 1
D=9/20+-2/5-1/3
D = 9 x 3 / 20 x 3 - 2 x 12 / 5 x 12 - 1 x 20 / 3 x 20
D = 27/60 - 24/60 - 20/60
D = - 17/60