a).13.860 cm b)10.395 cm c)6.930 cm d)3.465 cm

Keliling = 2 x π x r
66 cm   = 2 x 22/7 x r
66 cm   = 44/7 x r
          r  = 66 cm x 7/44
          r  = 10,5 cm

Volume kerucut
= 1/3 x π x r² x t
= 1/3 x 22/7 x 10,5 cm x 10,5 cm x 30 cm
= 3.465 cm³