## Thinking Mathematically (6th Edition)

Angles $2$ and $40^\circ$ add up to $90$ degrees thus Angle $2$ is $90-40=50^\circ$. Angles $1$, $2$ and $40^\circ$ add up to $180$ degrees thus Angle $12$ is $180-50-40=90^\circ$. Angle $3$ is $40^\circ$ plus angle $1$ because both the lines making the angle up are parallel to that angle, thus it is $90^\circ+40^\circ=130^\circ.$