Пошаговое объяснение:
x - ushburish
y - tortburish
x+y = 15 x=15-y
3x+4Y = 53
zamenyaem x
3(15-y) +4y = 53
45 - 3y + 4y = 53
y = 53-45 = 8
x=15-y = 15 - 8 = 7
