Hey there! :D
When finding x in shapes, we want to look for a congruence in angles.
We can find congruence by knowing a few basic rules about shapes, angles, symbols, etc.
By the tick marks on the right and left side of the trapezoid, we know that those sides are equal in length. By the triangles on the top and bottom of the trapezoid, we know that the two sides are congruent.
Since we know that both sides are congruent/and or equal in length, we can infer that the trapezoid's angles have specific congruent relations to one another that we can use to the find the angle marked by (x).
We know that any polygon with four angles will equal 360 degrees. We know one angle. We also know that adjacent angles are congruent. So, the angle across from (78) is also (78).
We can use this information to find x. Let the unmarked angle in the corner be called x as well.
78+78+x+x= 360
156+2x= 360
2x=204
x=102
I hope this helps!
~kaikers
