AA Similarity Postulate - we get the triangle on the left's angles; 90 and 63, and we subtract from 180.
180 - 90 - 63 = 27
So we have angle measures 27, 63, 90
For the triangle on the right, with measures 27 and 90, we use the same idea:
180 - 90 - 27 = 63.
You'll see that we also have 27, 63, 90.
Triangles with the same angles are defined as similar, so AA should be the answer
