1. 4
2. 12
3. 6
4. 18
5. 2
6. 4
7. 7
8. 15
9. 9
Answer: 
Step-by-step explanation:
The missing figure is attached.
For this exercise it is important to remember that, by definition, the opposite interior angles of an inscribed quadrilateral are supplementary, which means that their sum is 180 degrees.
Based on this, you can identify that the angle D and the angle B are opposite and, therefore, supplementary.
Knowing that, you can write the following equation:

Now you must solve for "x" in order to find its value. This is:

Then:

You know that:

Therefore, since you know the value of "x", you can substitute it into
and then you must evaluate, in order to find the measure of the angle A. This is:

Parallel slope = 2
This is because the original line has slope 2. Parallel lines have equal slopes.
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Perpendicular slope = -1/2
The original slope 2 or 2/1 turns into -1/2 after flipping the fraction and the sign. Note the original slope and perpendicular slope multiply to -1. This is true for any pair of perpendicular lines where neither line is vertical.