Base area of the tank = 80 × 50 = 4000 cm².

• Initially 75% full, then water poured out until 25% full.
• Fraction of water poured out = 75% − 25% = 50% of the tank.
• 50% of tank = 64 litres = 64000 cm³.
• 100% of tank = 64000 × 2 = 128000 cm³.
• Height = Volume ÷ Base area = 128000 ÷ 4000 = 32 cm.

Final Answer: 32 cm