As I recall, the angles of a triangle always add up to 180 deg.  In a right triangle, the one angle is always 90 dge; that means the sum of the other two angles must also add up to 90 deg.

One way to determine angles is to use the sine, cosine, tangent functions.  Maybe this little webpage can help refresh your memory. At the bottom of that webpage is a link to solving triangles".  Click on that link, and go to that page.  I think that next page should help refresh your memory, and help you find what you want to know.