Question

What is the value of x in trapezoid abcd

Answer 1

9x + 3x = 180.
12x = 180
x = 15.

Answer 2

x=15

Explanation:

Because CD║BA and BC≡AD,

Then: ∠B=∠A and ∠C=∠D.

All for corners must add up to 360°:

∠A + ∠B + ∠C + ∠D = 360

2∠B + 2∠D = 360

2(3x) + 2(9x) = 360

6x + 18x = 360

24x = 360

x = 15