The diagram provided is an isosceles triangle. An isosceles triangle has two sides having equal measure and two base angles also having equal measure.
From the marks on the triangle given, line ZX and line ZY are equal in length. This also means angle X and angle Y are equal in measure.
Therefore, we would have;
This means angle X and angle Y both equal 27 degrees each.
Note that the sum of angles in a triangle is 180. Therefore, in triangle ZXY,