Hello there. To solve this question, we'll have to remember some properties about vertical angles.
Given two angles A and B, they are said to be vertical angles if and only if:
That is, their measures are the same.
In this question, we have that the angles A and B have measures respectively equal to:
![m\angle A=\lparen2x-10)^{\circ\text{ }}=m\angle B=\left(x+8\right)^(\circ)](https://img.qammunity.org/2023/formulas/mathematics/college/rci3qvn1xil1zlae9fixfbawf88d8nm9ge.png)
Solving this equation for x:
Subtract x on both sides of the equation. Add 10 in the same manner.
![\begin{gathered} 2x-10-x+10=x+8-x+10 \\ x=18 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/wgxx2ga2g6v2pyz2hveu0s617zw833l25h.png)
Therefore we have the solution for x.
Now we plug this into A in order to find its measure:
![m\angle A=\left(2\cdot18-10\right)^(\circ)=\left(36-10\right)^(\circ)=26^(\circ)](https://img.qammunity.org/2023/formulas/mathematics/college/ro1daksnve45u0wqa27925jwgy4kva01dz.png)
This is the answer to this question.