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여기서 (a)번은 5.36×2.54=13.6144여서 반지름이 6.81인데,  (b)번부터 4×(6.81cm)^2을 했을때 제 답(185)이랑 답안이랑 너무 동떨어져 있는데 어떻게 계산해야 저 답이 나오는지 아시나요