Tolong bantu jawab nomor 6-9 Pake cara ... Terima kasih

 7. πr² x 2 + πr²
 = 38,5 x 2 + 154
= 231 cm

8. 12 x 8 + 1/2 (8+2) x (20-12)
= 96 + 40
=136 cm

9. 28² - π14²
= 784 - 616
= 168 cm