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sdt AOB per sdr BOC = bsr AB per bsr BC
sdt AOB per 90 = 60 per 45
sdt AOB = 60 per 45 kali 90
sdt AOB = 120 (C)

bsr AB = (sdt AOB per 360) kali keliling lingk
sdt AOB = (360 kali bsr AB) per Keliling lingk
sdt AOB = (360*22) / (22/7 * 28)
sdt AOB = 90 (B)