perhatikan gambar di samping sudut ABD adalah

total = 180 = 7x+5x
7x+5x = 180
12x = 180
x = 15
ABD = 7X = 7 × 15 = 105

Diketahui
ABD = 7x°
DBC = 5x°

180° = ABD + DBC
180° = 7x° + 5x°
180° = 12x°
x = 180/12
x = 15

Sudut ABD
= 7x°
= 7 . 15°
= 105°

semoga membantu :)