Well, we said A and B were complimentary angles and if we notice, they sum to 90
degrees or a right angle. You usually draw a box in the corner to indicate a
right angle. If I want to find angle D, I know C and D have to add up to 90
degrees. I know C is 55 degrees. So, if I just subtract 55 from both sides,
angle D is 35 degrees. We can use the exact same process for angle E and angle
F. If I subtract 12 degrees from 90, I get 78 degrees. If you figured out what
complementary meant, nice work. If not, that's okay. Hopefully, you'll learn
along the way.