Пошаговое объяснение:
4/40 + y + 16/40 = 31/40 + 6/40
20/40 + y = 37/40
y = 37/40 - 20/40
y = 17/40
4/40 + 17/40 + 16/40 = 31/40 + 6/40
21/40 + 16/40 = 37/40
37/40 = 37/40
