jawab nomor 12 pakai cara please!!

Sudut pelurus = 180°
7x + 8 + 5x + 4 = 180°
12x + 12 = 180
12x = 180-12
12x = 168
X = 168/12
X = 14 (A)

(7x + 8)° + (5x + 4)° = 180°
7x + 5x + 8 + 4 = 180°
12x + 12 = 180°
12x = 180 - 12
12x = 168°
x = 168 : 12
x = 14

Jawabannya a