C. 128 degrees, Alternate interior angles theorem. Brainliest? Hope this helped!
Answer:

Step-by-step explanation:
1. Create an equation
<em><u>Concept</u></em> :
If x = 5, then subtracting 5 from both sides gives you x - 5 = 0. Do this to both variables
If x - 5 = 0 and y - 12 = 0, those two statements equal the same thing. So

2. Add 5 to both sides to isolate variable X

3. (Optional) Plug given values into new equation to check answers

5 = 5 is a true statement