Step-by-step explanation:
[tex]\angle 3[/tex] and [tex]\angle 16[/tex] are alternate exterior angles so they are equal to each other, which means
[tex]5x - 30 = 3x + 10 \Rightarrow x = 20[/tex]
Solving for the measure of [tex]\angle 16[/tex], we get
[tex]m\angle 16 = 5(20) - 30 = 70°[/tex]
Since [tex]\angle 12[/tex] and [tex]\angle 16[/tex] are supplementary,
[tex]m\angle 12 = 180° - 70° = 110°[/tex]
