we have angle 9 and angle 10 are collateral angles, this means that they are supplementary, i.e. they add up to 180°. Therefore:
[tex]\begin{gathered} m\angle9+m\angle10=180 \\ m\angle9+77=180 \\ m\angle9+77-77=180-77 \\ m\angle9=103 \end{gathered}[/tex]
answer: m<9 = 103°
