Tolong dijawab ya plis, pake cara, mksh

Nomor 7
<COB + <AOB = 90°
4a + 18 + 2a = 90
6a = 90-18
a = 12

<COB = 4(12)+18 = 66°

nomor 8
<KLN + <NLM =180°
(3x+15) + (2x+10) =180
5x = 180-10-15
5x = 155
x = 31
<KLN = 3(31) + 15 =93+15 = 108°

SEMOGA MEMBANTU YA, MAAF KALO SALAH :3 (duh yang nomor 9 kurang ngerti, maaf ya)