I think the scale factor of one block to the arrangement would be 1/9, since the arrangement contains 9 blocks.
So if the length at the top is 12 cm, the length of the bottom of a trapezoid would be 12(1/9) = 4/3
Since we know that each trapezoid holds 3 equilateral triangles, the length of each side and the top of the trapezoidal would be 4/3 x 1/2 = 2/3 cm
The sum of the angles must equal 360 degrees, and because they are made of equilateral triangles, you know that each angle of the triangle must be 60 degrees. So the bottom two angles of the trapezoid are each 60 degrees, and the top two are 360- 120 = 240 divided by 2 angles = 120 degrees each.
