jawab dan pakai cara

2x + 3y = 180°
2x + y = 90°
____________ -
2y = 90
y = 45°

2x + y = 90°
2x + 45° = 90°
2x = 45°
x = 22,5°

.

x + y = 22,5° + 45° = 67,5° (c)