Question

What is the value of x in trapezoid ABCD? X = ?

Answer 1

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

Answer 2

we know that

In the isosceles trapezoid of the figure, the angles on either side of the bases are the same size/measure (congruent), and adjacent angles (next to each other) along the sides are supplementary.

so

m∠A=m∠B=3x

m∠D=m∠C=9x

m∠A+m∠D=$180$

Substitute

$3x+9x=180\\\\ 12x=180\\\\ x=\frac{180}{12} \\ \\ x=15\ degrees$

therefore

the answer is

the value of x is equal to $15\ degrees$