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=[tex] 180 [/tex]
Substitute
[tex] 3x+9x=180\\\\ 12x=180\\\\ x=\frac{180}{12} \\ \\ x=15\ degrees [/tex]
therefore
the answer is
the value of x is equal to [tex] 15\ degrees [/tex]
