Remember the sum of the angles in a triangle is equal to 180
so to find the missing angle we subtract the given angles from 180
180 - 34 - 90 = 56
so we can conclude that the measure of the missing angle is 56 degrees
Note: the little square at the bottom left of the triangle indicates that the angle is a right angle. The measure of a right angle is 90 degrees so thats where the 90 came from