Is this correct? (psat math)?

Question

http://tinypic.com/view.php?pic=1zoc6s3&s=4

I got D...

Answer 1

The Answer is C.

The value of n is equal to the sum of the opposite interior angles (a and b), which means the answer is C -- a + b

Answer 2

I'm pretty sure it's C.  Since there aren';t parentheses, D is like saying it's 180- A, and then adding the value of B. You were right about the unknown angle being 180-n.

Answer 3

The answer is C

The sum of the three angles in a triangle total 180 degrees. In this case, we have angles (180-n), a, and b.

(180-n)+a+b=180

-n+a+b = 0

a+b = n

So C