(6, 31+2pi degrees)
(6, 31+4pi degrees)
(-6, 31-pi degrees)
(6, 31-2pi degrees)
etc. etc.
The prallelogram whose adjacent sides are equal and one vertex angle is 90 degrees is a square.
The value of angle 1 is 90 degrees as the diagonal of the square intersect at 90 degrees.

The value of y is 23.
The diagonal of the square bisect the vertex angle hence the angle of 3x is 45 degrees.

Thus, the value of x is 15 degrees.
The value of 12z is 45 degrees.

Thus, the required value of z is 3.75 degrees.
Answer:
We use cosine rule also called cosine law which states
c^2=a^2+b^2-2abcosC
given
a=8cm, b=7cm, c=9cm cos C?
9^2=8^+7^2-2*8*7 cos C
expand
81=64+49-112 cos C
like terms together
81-113=-112 cos C
-32=-112cos C
multiply both sides by -1
32=112cos C
divide both sides by 112
32/112=cos C
cosC=0.2857
find cos inverse of 0.2857
angle C= 73.40
The first one is correct I think.