Answer:
137°
Explanation:
The pentagon RSTYZ is a regular polygon. Therefore all angles are congruent.
If m∠RST = 108°, then m∠STY = 108°.
We have the equation:
m∠UTY + m∠STY + m∠STU = 360°.
Substitute m∠STY = 108° and m∠UTY = 115°.
115° + 108° + m∠STU = 360°
223° + m∠STU = 360° subtract 223° from both sides
m∠STU = 137°