If two angles of one triangle are congruent to two angles of a second triangle, then the third angles of the triangles are congruent.
According to the theorem, since our triangles share two angles, the third angles of these two triangles are also congruent.
∠ G≅∠ C
This means that these angles have the same measures so m∠ G is equal to m∠ C. Notice that the measure of ∠ C and an expression for the measure of ∠ G are given. Therefore, by using the congruence, we can set up an equation for x.
