1=45 2=135 3=135 6=45 7=45 8=135 9=90 12=90 4 and 1 are opposite, and thus equal, angles. 7 and 5 are supplementary angles, and thus they add up to 180 degrees. To get 7, you subtract 135 degrees from 180. 9 and 10 are supplementary and equal since all four those angles are 90 degrees.
