Total volume = Edge³. Half-filled initially.

• Total volume = 10 × 10 × 10 = 1000 cm³ = 1000 ml
• Initially half full = 1000 × \(\frac{1}{2}\) = 500 ml
• Final volume = \(\frac{4}{5}\) × 1000 = 800 ml
• Water added = 800 − 500 = 300 ml

Final Answer: 300