Answer:
Since [tex]A \parallel B[/tex], we know [tex]m \angle3 = 4x + 5[/tex] since they are corresponding angles. Then since [tex](3x + 7) + m\angle 3 = 180[/tex] (supplementary), we can substitute to get
[tex](3x + 7) + (4x + 5) = 180[/tex]
[tex]7x + 12 = 180[/tex]
[tex]7x = 168[/tex]
[tex]x = \boxed{24}[/tex]
We know [tex]m\angle 6 = 3x + 7[/tex], since they are corresponding angles, so
[tex]m \angle 6 = 3(24) + 7 = \boxed{79}[/tex]
