Answer: x = 40
have: ∠A + ∠B + ∠C + ∠D = 180°
⇔ x + 6 + x + 4 + x +10 + x = 180°
⇔ 4x + 20 = 180
⇔ x = (180 - 20)/4
⇔ x = 160/4 = 40
Explanation:
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