Tolong kak... Bagaimana caranya mencari keliling no. 4 dan no. 5

4. kllng = 2Πr:2 diameter=42>r=21
= 2×22/7×21:2
=2×22×3:2 > (21:7=3)
= 132:2 = 66cm
5. kllng = 2Πr3/4
= 2×3,14×25×3/4
= 6,28 × 25 × 3/4
= 471 : 4
= 117,75cm