As shown in the figure, fold △ ABC along De, if ∠ 1 + ∠ 2 = 80 °, then ∠ B=______ Degree

∵△ ABC is folded along the de, with ∠ 1 + 2 ∠ bed = 180 °, 2 + 2 ∠ BDE = 180 °, 1 + ∠ 2 + 2 (∠ bed + ∠ BDE) = 360 ° and ∠ 1 + ∠ 2 = 80 °, B + ∠ bed + ∠ BDE = 180 °, 80 ° + 2 (180 ° - b) = 360 ° and ∠ B = 40 °. So the answer is: 40 °

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