The sum angles in a triangle is 180 degrees
In the first triangle where we have 36 degrees and 63 degrees
we have three angles
36 degrees , 63 degrees and x degrees
x + 36 + 63 = 180
x + 99 = 180
isolate x
x = 180 - 99
x = 81 degrees
to calculate z
interior altenate angles are equal
36 degrees is alternate to angle z
Therefore 36 degrees = z
z = 36 degrees
to get y
y + 36 + 13 = 180
y + 49 = 180
y = 180 - 49
y = 131 degrees