Hello!
Since the angles are alternate interior angles they equal each other
5x - 28 = 3x + 12
Now you solve this algebraically
5x - 28 = 3x + 12
Subtract 3x from both sides
2x - 28 = 12
Add 28 to both sides
2x = 40
Divide both sides by 2
x = 20
Now we put x into the equation we are wanting to find out
5x - 28
5(20) - 28
Multiply
100 - 28
Subtract
72
The answers are x = 20 and 5x - 28 = 72°
Hope this helps!