Answer:
idk if i have this right, but i believe it is "Segment Addition Postulate". the 2 sets given are congruent. and considering they are asking if the whole thing is congruent, and the 2 parts are congruent, then 2+2=4, quite literally. :P
please keep in mind that i may not be right, but it seems like the most likely answer. let me know if im wrong, please!
