Answer: a = 35
Step-by-step explanation: The answer would be 35 because we already know one of the angles is 55 degrees and the other would be 90 degrees because the little square gives it away. Now, all you need to do is add 55 and 90 which would give you 145. Since the line is 180 degrees you would have to subtract 145 from 180 which would give you 35.