Answer:
![m\angle 4=40^(\circ)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/x2vkornyhl10pntdr0zzljjcn685d9glw5.png)
Explanation:
Angles 6 and 7 are vertical angles (opposit to each other). Vertical angles are congruent, so
![11x+8=12x-4\\ \\11x-12x=-4-8\\ \\-x=-12\\ \\x=12](https://img.qammunity.org/2020/formulas/mathematics/middle-school/jyqdj5wscxwljh30cgwivcnsmvnideb3po.png)
Now,
![m\angle 6=(11\cdot 12+8)^(\circ)=140^(\circ)\\ \\m\angle 7=(12\cdot 12-4)^(\circ)=140^(\circ)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/e62i9mn8uq4eiqajnes9iacqv7i2ljzggq.png)
Angles 6 and 8 are supplementary angles (add up to 180°), so
![m\angle 8=180^(\circ)-140^(\circ)=40^(\circ)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/xwbfwos43xc1z1gzjatho8s7rkg4mqqkih.png)
Angles 8 and 4 are corresponding angles. Corresponding angles are congruent, so
![m\angle 4=40^(\circ)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/x2vkornyhl10pntdr0zzljjcn685d9glw5.png)