AD/AB = 1/3 => AB=3AD si AB=15 cm => AD=5 cm, iar DB = 10 cm
DE || BC => ΔADE ~ ΔABC => AD/ AB, iar = AE/AC = DE/BC (TFA)
=> 5/15 = AE/18 = DE/12 => AE = 6 cm (=> EC = 12 cm), iar DE = 4 cm
DE || BE si DB nu e paralela cu EC => BCED trapez
P = DB + BC + CE + DE = 10 + 12 + 12 + 4 = 38 cm