1 and 3 are congruent and so are 2 and 4. (Congruent means they have the same degrees.)
Sense we know <2 is 73 degrees let's break it up. 1 and 2 are on the same line, (a line is equal to 180.) So if we take <2 sense we know the degree is 73-180=<u>107</u><u> </u><u>.</u> We do this so we can find the other angles degree.