The sum of the angle of a triangle is 180 degrees. It is mentioned that Hannah drew a pattern of equilateral triangles. Equilateral triangle has three equal sides. Also, its angles are the same, having 60 degrees at each corner of the triangle. The answer is a. Letter b does not qualify to be an equilateral triangle because 120 degrees times 3 is greater than 180 degrees. Letter c and d exceeds the total number of angles at 180 degrees.