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Volume = 1/3 x π x r² x t
9π dm³ = 1/3 x π x r² x 8 dm
  9 dm³  = 8/3 dm x r²
          r² = 9 dm³ x 3/8 dm
          r² = 3,375 dm²
          r  = √3,375
          r  = 1,83 dm

s = √t² + r²
   = √8² + 1,83²
   = √64 + 3,375
   = √67,375
   = 8,20 dm

Luas permukaan kerucut
= π x r ( r + s )
= π x 1,83 dm ( 1,83 dm + 8,20 dm )
= 1,83π dm x 10,03 dm
= 18,354π dm²