D = 3 - 20/21 x 7/5
D = 3 - 140/105
D = 3 x 105 / 1 x 105 - 140/105
D = 315/105 - 140/105
D = 175/105
D = 35 x 5 / 35 x 3
D = 5/3
E= (2/7 - 1/3) x 7/4 - 5/4
D = (2 x 3 / 7 x 3 - 1 x 7 / 3 x 7) x 7/4 - 5/4
D = (6/21 - 7/21) x 7/4 - 5/4
D = - 1/21 x 7/4 - 5/4
D = - 7/84 - 5/4
D = - 7/84 - 5 x 21 / 4 x 21
D = - 7/84 - 105/84
D = - 112/84
D = 28 x - 4 / 28 x 3
D = - 4/3
F = 1/45 : 4/9 + 7/3
F = 1/45 x 9/4 + 7/3
F = 9/180 + 7/3
F = 9/180 + 7 x 60 / 3 x 60
F = 9/180 + 420/180
F = 429/180
F = 3 x 143 / 3 x 60
F = 143/60
G = (- 5/6 + 3/4) : (7/6 - 6/7)
G = (- 5 x 4 / 6 x 4 + 3 x 6 / 4 x 6) : (7 x 7 / 6 x 7 - 6 x 6 / 7 x 6)
G = (- 20/24 + 18/24) : (49/42 - 36/42)
G = - 2/21 : 13/42
G = - 2/21 x 42/13
G = - 84/273
G = 21 x - 4 / 21 x 13
G = - 4/13
