∮ geo = ∮ oef, ∮ hfo = ∮ ofe,
∵ GH ∲ ef,
∮ GoE = ∮ oef, ∮ Hof = ∮ ofe,
∮ geo = ∮ GoE, ∮ Hof = ∮ hfo,
∮ ge = go, oh = HF,
∯ dgh ∯ 둘레 = DG+GO+DH+HO = DE+DF = 15.
그래서 대답은: 15 입니다.