А)
х + 4/15 = 2/3 + 2/5
х = 2/3 + 2/5 - 4/15
х = (10 + 6 - 4)/15
х = 12/15
х = 4/5
б)
(4/5 - х) + 13/20 = 25/30
4/5 - х + 13/20 = 25/30
-х = 25/30 - 4/5 - 13/20
-х = (50 - 48 - 39)/60
-х = -37/60
х = 37/60
в)
у - 5/20 = 5/8 - 3/10
у = 5/8 - 3/10 + 5/20
у = (25 - 12 + 10)/40
у = 23/40
г)
2/3 - ( 7/9 - а) = 1/3
2/3 - 7/9 + а = 1/3
а = 1/3 - 2/3 + 7/9
а = (3 - 6 + 7)/9
а = 4/9