The radius of the small semicircle is 3cm, the arc length is 3. 14x3=9.42cm, and the area is 3. 14x3? x 1/2= 14. 13cm？

The radius of the big semicircle is 5cm, the arc length is 3. 14x5= 15.7cm, and the area is 3. 14x5? x 1/2=39.25cm？

Shadow area (ring area) = 39.25-14.13 = 25.12cm?

The perimeter of the shaded part is 9.42+15.7+(5-3) x2 = 29.12cm.