Answer:
60
The angle acute so my guess is 60
Hope this helps :)
In order to do this you have to substitute b with 9 and get 3a+9=54, now subtract 9 from both sides to leave a by itself and get 3a=45, now divide 3 in both sides to leave a by itself and get a=15
Hope this helps
The supplementary angle would be 180 degrees, and the other angle would be 92.2 degrees
