To solve that question we must remember that the sum of all internal angles of a triangle is 180°, we can say that
![\angle X+\angle Y+\angle Z=180](https://img.qammunity.org/2023/formulas/mathematics/college/xiet6n06bl51j1438cm3uyiyhi0rv7ml60.png)
That's a rule! it's always true.
The problem says that
![\angle X+\angle Y=55](https://img.qammunity.org/2023/formulas/mathematics/college/fn5ufjqqs8mo2eyz4vqdgxdbjp65263vn6.png)
Then let's use it in our equation!
![\begin{gathered} \operatorname{\angle}X+\operatorname{\angle}Y+\operatorname{\angle}Z=180 \\ \\ 55+\operatorname{\angle}Z=180 \end{gathered}]()
Now we can solve it for Z
![\begin{gathered} 55+\angle Z=180 \\ \\ \angle Z=180-55 \\ \\ \angle Z=125° \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/fhoegjatjm73i3dlt6f2ze0kml7dsdtiht.png)
Therefore the measure of Z is 125°