1 and 2 are vertically opposite angles and hence they must be equal.
[tex] \sf \: m \angle1 \: = m\angle2 \\ \sf \longrightarrow 6x + 12 = 9x - 4 \\\sf \longrightarrow9x - 6x = 12 + 4 \\\sf \longrightarrow3x = 16 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \\\sf \longrightarrow \: x = \frac{16}{3} \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \\\sf \longrightarrow \: x = 5. \overline{3} \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \\\sf \leadsto \: \underline{ \boxed{ \sf{ \color{deeppink} \: {x \approx \: 5.3 \: }}}}\: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: [/tex]
