The sum of all three angle measures in a triangle will always equal 180 degrees. So, if you subtract 63 and 27 from 180 you will have your third angle measure, which is 90.
So now your 3 measures are 63, 27, and 90. Since one of the angles is a 90-degree angle, the triangle must be a right angle because a right angle has a measure of 90 degrees.