All sides are the same length (congruent) and all interior angles are the same size (congruent). To find the measure of the angles, we know that the sum of all the angles is 1080 degrees (from above)... And there are eight angles... So, the measure of the interior angle of a regular octagon is 135 degrees
For the perimeter you have to consider the EXTERNAL SHAPE ONLY:
a) the perimeter of half a circle WITHOUT ITS DIAMETER is: π.R - 2R → 3.14x1.5 - 2x1.5 → 1.71 cm
b) the perimeter of the rectangle WITHOUT THE UPPER SIDE is: 2.5+3+2.5 = 8 cm
Hence the perimeter of the figure is 1.71 + 8 = 9.71 cm
2) Area of the figure: Area of half circle is π.R²/2 →3.14 x (1.5)²/2 → Area half circle = 3.5325 cm² Area of rectangle = 2.5 x 3 = 7.5 cm² Total area = 3.5325 + 7.5 = 11.0325 ≈ 11 cm²