The first figure is a rectangle. Rectangles are known for having four right angles. Thus, one of the angles in this figure is 90 degrees.
The second figure is an equilateral triangle. Because all its sides have the same length, the angles are all the same. There is a principle stating that the sum of the 3 interior angles of a triangle is 180 degrees. Thus, the measure of one of these 3 angles is 180 degrees / 3 = 60 degrees.
