On the diagram we can see two triangles. Let's shade these.
Notice that these triangles have a common side, and according to the information given on the figure, the other two sides are congruent.
According to the Side-Side-Side (SSS) Congruance Postulate the blue and green triangles are congruent. We know that corresponding angles in congruent triangles are congruent. We can use this to set the two given angle expressions equal to each other and solve the resulting equation for x.
