Explanation:
it is a parallelogram.
that means both pairs of opposite sides are parallel and the sides of each pair are equally long.
the sum of all internal angles is 360°.
the opposing angles are equal.
and therefore neighboring angles are complementary angles (or a linear pair) : together they have 180°.
so,
76 = 4x - 8
84 = 4x
x = 21
-3z + 8 + 76 = 180
-3z + 84 = 180
-3z = 96
z = -32
-3z + 8 = -6y - 10
-3×-32 + 8 = -6y - 10
96 + 8 = -6y - 10
104 = -6y - 10
114 = -6y
y = -19