Х + 4/15 = 2/3 + 2/5

(4/5 - х) + 13/20 = 25/30

у - 5/20 = 5/8 - 3/10

2/3 - (7/9 - а) = 1/3

Х=2/3+2/5-4/15

х=12/15+4/15=16/15

(4/5-х) = 25/30-13/20=500-390/600=110/600=11/60

х=4/5-11/60=48-11/60=37/60

у=5/8-3/10+5/20

у=23/40

(7/9-а) = 2/3-1/3

(7/9-а) = 1/3

а=7/9-1/3

а=7-3/9=4/9

Х + 4/15 = 2/3 + 2/5

х + 4/15 = 10/15 + 6/15

х + 4/15 = 16/15

х = 16/15 - 4/15

х = 12/15 = 4/5

4/5 + 4/15 = 2/3 + 2/5

12/15 + 4/15 = 10/15 + 6/15

16/15 = 16/15

Ответ: х = 4/5

(4/5 - х) + 13/20 = 25/30

4/5 - х = 25/30 - 13/20

4/5 - х = 50/60 - 39/60

4/5 - х = 11/60

х = 4/5 - 11/60

х = 48/60 - 11/60

х = 37/60

(4/5 - 37/60) + 13/20 = 25/30

(48/60 - 37/60) + 13/20 = 25/30

11/60 + 13/20 = 25/30

11/60 + 39/20 = 25/30

50/60 = 25/30

25/30 = 25/30

5/6 = 5/6

Ответ: х = 37/60

у - 5/20 = 5/8 - 3/10

у - 5/20 = 25/40 - 12/40

у - 5/20 = 13/40

у = 13/40 + 5/20

у = 13/40 + 10/40

у = 23/40

23/40 - 5/20 = 5/8 - 3/10

23/40 - 10/40 = 25/40 - 12/40

13/40 = 13/40

Ответ: у = 23/40

2/3 - (7/9 - а) = 1/3

7/9 - а = 2/3 - 1/3

7/9 - а = 1/3

а = 7/9 - 1/3

а = 7/9 - 3/9

а = 4/9

2/3 - (7/9 - 4/9) = 1/3

2/3 - 3/9 = 1/3

6/9 - 3/9 = 1/3

3/9 - 1/3

1/3 = 1/3

Ответ: а = 4/9