The given figure is an isosceles trapezoid. The base angles are marked with $y^\circ$, indicating they are equal. The two non-parallel sides are marked with single hash marks, indicating they are equal in length. The two angles formed between the non-parallel sides and the longer base are marked with $x^\circ$. The sum of the interior angles of a quadrilateral is $360^\circ$. The markings on the sides of the two triangles within the trapezoid indicate they are isosceles. The base angles of the two isosceles triangles are congruent.
Step 2: Set up an equation
The sum of the interior angles of a trapezoid is $360^\circ$. We have two angles measuring $y^\circ$ and two angles measuring $x^\circ$. Therefore, $2x + 2y = 360$.
Step 3: Simplify the equation
Divide both sides of the equation by 2:
$x + y = 180$