Answer:
20
Explanation:
side BC = side AB
so their base angles that is ∠A = ∠C = (3x+20)°
now, total measure of the angles of a triangle is 180° & ∠B = x°
Now,
m∠A + m∠B + m∠C = 180
⇒ 3x + 20 + x + 3x + 20 = 180
⇒ 7x + 40 = 180
⇒ 7x = 140
⇒x = 20
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