This is hard to kind of type out description on how I do it for me but here goes. (I’m actually 12 :P) since the angle on the opposite side of the 107* obtuse angles it would also be 107*. On the angle right below angle a it would also be 107* because of opposite angle relationship (I forgot the actual name) For angle a there is a way that I find easy to find the angle, with supplementary angle. There might be another way but this is how I do it. I subtract 180-107 because 180* is a line then I get angle a, 73*. Using that opposite angle thing the angle identical to angle a is also 73, also is the one beside the 107* degree obtuse angle. You add 73+73 (73*2) and get 146. Then subtract 180-146. Hope that was helpful good luck!
