kak tolong diselesaikan besok sudah dikumpul plisss

1. y+6 = 18-2y
3y = 12
y = 4
2. 6x+6 = 7x+4
-x = -2
x = 2
3. 16a-5 = 4a+7
12a = 12
a = 1
4. 5+15z = 7z+21
8z = 16
z = 2