S△ABE = 8 , ,S△DEF = 3
S◇ABCD = 4S△ABE = 32
E是AD的中点 S△DCE = S△ABE = 8
S△CEF = S△CDE - S△DEF = 5
CF / DF = S△DCE / S△DEF = 5 / 3
CF / CD = 5 / 8
S△BCF = (5 / 16)S◇ABCD = 10
S△BEF = S◇ABCD - S△ABE - S△DEF - S△BCF = 11
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