Because we know the triangles are similar and the angle of D = angle of A, that means that the angle of B = angle of E and angle of C = angle of F. Therefore, angle of C = 78 degrees and angle of E = 64 degrees. The angles of a triangle sum to 180 degrees, so we have the equation: x + 64 + 78 = 180. Solving for x gives you x = 38 degrees, which is the same as angle y.