Answer:
a = 60
Step-by-step explanation:
First off this is a straight angle so it will add up to 180 degrees we already have 30 and the other angle between a and 30 is a 90 degree angle so now we just have to subtract those from 180 to get the answer! so... 90 + 30 = 120 180 - 120 = 60
So 60 is the answer hope that helps!
