I assume that by square corners you mean 90 degree angles. if this is the case then there are 2 in a pentagon. Hope I helped :)
Answer:
∠ XZY ≈ 23.6°
Step-by-step explanation:
Using the sine ratio in the right triangle
sin Z =
=
=
, thus
Z =
(
) ≈ 23.6° ( to 1 dec. place )
I believe the answer should be 77