Answer:
To answer this question we will use the following diagram as reference:
Recall that the interior angles of an equilateral triangle measure 60 degrees each.
Now, notice that angles A and B form a linear pair, meaning that:
![\angle A+\angle B=180^(\circ).](https://img.qammunity.org/2023/formulas/mathematics/college/qnis4nwxrw6ncumg357qtmds4g2r6og1hw.png)
Substituting ∠A=60°, ∠B=8x° in the above equation we get:
![60^(\circ)+8x^(\circ)=180^(\circ).](https://img.qammunity.org/2023/formulas/mathematics/college/6nb9gdl0wvk2qf6xg8pecrtjun31mt201q.png)
Solving the above equation for x, we get:
![\begin{gathered} 60+8x=180, \\ 8x=180-60=120, \\ x=(120)/(8), \\ x=15. \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/5d52t9u7f0hjgcjtbwftobpr41uxd8n3uj.png)