Explanation:
I assume these are all angles.
4x is the arc angle (at the center of the circle) between the 2 endpoints of the short triangle side (baseline).
the trials itself is isoceles, so both legs have the same length, bedclothes the arc angles between their endpoints are equal.
now, when we move the reference point of an arc angle back, back, back to the circle arc, the angle is cut in half.
so, the inner top angle of the triangle is therefore 4x/2 = 2x.
because of the isoceles nature, the second triangle inner angle at the baseline is also x.
the sum of the triangle angles is therefore
2x + x + x = 4x
and we know the sum of all angles in a triangle is always 180°.
so,
4x = 180
x = 180/4 = 45°
4x is then again 180°, and 2× 8y are then the remaining 180° of the full circle 360°.
2× 8y = 180
8y = 90
y = 90/8 = 11.25
x = 45
y = 11.25