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volume = πr²t
12320= 3,14 x r² x 20
12320 = 62,8 x r²
r²= 12320/62,8
r²= 196,18
r=14 cm
luas permukaan = 2πr(r+t)
=2 x 3,14 x 14 (14+20)
=87,92(34)
=2989,28 cm²