The triangle in the picture is an equilateral triangle. We know this is true because all sides are equal, as denoted by the tick marks. In equilateral triangles, each angle is 60° because when you add all the angles, you get 180°.
One way to solve this is to look at the size of the poster, and then subtract the size of the picture so you have the area that needs to be painted left.
Area of square poster - 3x × 3x = 9x^2 Area of painting - 2x × 2x = 4x^2
