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4.
rusuk = 70 cm = 7 dm
Volume = rusuk³
             = 7³
             = 343 dm³
             = 343 Liter

Sisa Volume = 343 - (343 x 4/5) = 343 - 274,4 = 68,6 Liter

5.
V.kubus = V.balok
rusuk³ = p x l x t
rusuk³ = 4 x 6 x 9
rusuk³ = 216
rusuk = ∛216
rusuk = 6 cm