Х + 4/21 = 2/3 + 2/7
х + 4/21 = 14/21 + 6/21
х + 4/21 = 20/21
х = 20/21 - 4/21
х = 16/21
у + 1/4 = 4/5 - 3/10
у + 1/4 = 8/10 - 3/10
у + 1/4 = 5/10 = 1/2
у = 1/2 - 1/4
у = 2/4 - 1/4
у = 1/4
(4/5 - х) + 13/20 = 7/10
4/5 - Х = 7/10 - 13/20
4/5 - Х = 14/20 - 13/20
4/5 - х = 1/20
х = 4/5 - 1/20
х = 16/20 - 1/20
х = 15/20 = 3/4
2/3 - (2/9 + х) = 1/3
2/9 + х = 2/3 - 1/3
2/9 + х = 1/3
х = 1/3 - 2/9
х = 3/9 - 2/9
х = 1/9