What is the length of stack m n with bar on top ? round to the nearest tenth of a unit

What number must you add to complete the square x^2+12x=16

Which is a true statement about an exterior angle of a triangle a. it is formed by two segments that are not sides of the triangle, b. it forms a linear pair with one of the interior angles of the triangle, c. it is complementary to one of the interior angles of the triangle. d. it is formed by two segments that are sides of the triangle.

Ill mark the brainliest if you me with the these three questions 7,8,9