0 because the number in the middle is the midpoint.
<h2>
Hello!</h2>
The answer is:

<h2>Why?</h2>
To solve the problem, remember to set your calculator in "degree mode"
So, we are given that the angle A is equal to 68°
So, we have that:

Hence, we have that:

Have a nice day!
The answer, is CD. The 3rd one
D.A plane consist of an infinite set of lines.