Answer: 23
Explanation:
This is another parallel line theorem that is important. Over here, we will need to use the concept of corresponding angles (refer to images below). In corresponding angles, they are equal. So we know the corresponding angle to
will be equal to
since corresponding angles are equal.
Now we have to use the fact that angles on a line add up to 180°. Keeping this in mind, we can now solve it like this:

Once again, if there is anything you don't understand, please reply back :)