2x + 15 = -27
2x = -27 - 15
2x = -42
x = -42 : 2
x = -21
2x + 15 = -27
2x = -27 - 15
2x = -42
x = -42 : 2
x = -21
2x + 15 = - 27
2x = - 27 - 15
2x = - 42
x = - 42 : 2
x = - 21
2x + 15 = -27
2x = (-27) - 15
2x = -42
2x = (-42) : 2
2x = -21
vậy x = -21