Those are two 30 60 90 triangles with a common side.
In the left triangle, x = 8 * sq root (3) / 2=
.75*8 = 6 (approximately)
sine (30) = opp/hyp = x/y =
.5 = [8*sq root (3) / 2] / y
y = [8*sq root (3) / 2] / .5
y = 8*sq root (3)
y = 12 (approximately)