We have to use the interior angles theorem, which states that the interior angles in a triangle must sum 180°.
[tex]\begin{gathered} 8x+x+90=180 \\ \end{gathered}[/tex]
Then, we solve for x
[tex]\begin{gathered} 9x+90=180 \\ 9x=180-90 \\ 9x=90 \\ x=\frac{90}{9} \\ x=10 \end{gathered}[/tex]
Hence, x is equal to 10°.
