Question 645178
Hello,

Supplementary angles means that the sum of the two angles is 180. 
Angle 'A' is 81.2. It asked for a supplement. Since the other angle is unknown, you take 180 and subtract it from 81.2 and you get  98.8 

180 - 81.2 = 98.8

The supplement of angle 'A' is 98.8
You check by adding the 2 angles and if you get 180, it's right!
I hope this helps!