Which of the following best estimates the amount of ice remaining in a cubical thermacole icebox with 30 cm sides and 5.0 cm thickness, after 6 hours, when initially filled with 4.0 kg of ice, and exposed to an outside temperature of 45°C, considering a coefficient of thermal conductivity of 0.01 J s ⁻¹ m ⁻¹ K ⁻¹ for thermacole and a heat of fusion of water equal to 335 × 10 ³ J k g ⁻¹ ?