Line A is parallel to line B and line C is parallel to line D, therefore angle 12 is congruent with angle 10, and angle 10 is congruent with angle 7. This pair of angles, (12 & 10, and 10 & 7) are congruent, which means their measure is the same because they're corresponding angles in parallel lines. Obviously, they aren't either supplementary or complementary; they are congruent. Trust me guys, that's the answer. I'm sure that someone will agree with me.