tolong cuma satu soal

lihat segitiga BDE
∠EBD + ∠BED + ∠EDB = 180
30 + (20+65) + a = 180
30 + 85 + a = 180
115 + a = 180
a = 180 - 115
a = 65°

∠BDC = ∠BEC (sudut keliling yang sama-sama menghadap busur BC)
b = 20°

lihat segitiga ECD
∠DEC + ∠ECD + ∠CDE = 180
65 + c + (65+20) = 180
65 + c + 85 = 180
150 + c = 180
c = 180 - 150
c = 30°