The perimeter of the shaded part is 3.93 cm.
Step-by-step explanation:
Step 1; The perimeter of a circle is calculated by multiply 2π with the radius. This given circle is not an entire circle. An entire circle has an angle if 360° while this has an angle of 50°. So we divide 360° with 50°.
Number of these shapes to form a full circle = 360° / 50° = 7.2. So 7.2 of these shapes will need to be combined to form a full circle. So we can calculate the perimeters of full circles and then divide it by 7.2 to get the parameters of the given sections.
Step 2; The parameter and circumference of a circle are equal. So
The perimeter of shaded region = Perimeter of the entire region - Perimeter of the unshaded region.
The Perimeter of circle with radius 8cm = 2π × 8 = 50.2654 cm.
The perimeter of the given shape = 
= 6.9813 cm
The perimeter of circle with radius, 3.5cm (8cm - 4.5cm) = 2π × 3.5 = 21.9911 cm,
The perimeter of unshaded region = 
= 3.0543 cm.
So the perimeter of shaded region = 6.9813 cm - 3.0543 cm = 3.927 cm.
Rounding 3.927 to 3 significant figures we get the perimeter of shaded region equal to 3.93 cm.
