Let Tank B contain 1 unit of water.

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• Tank A = 4 units (4 times Tank B)
• Tank C = 4 units − 150 litres (150 less than Tank A)
• Total = 1 unit + 4 units + (4 units − 150) = 9 units − 150
• 9 units − 150 = 1350
• 9 units = 1350 + 150 = 1500
• 1 unit = 1500 ÷ 9 = 166 \(\frac{2}{3}\)

Tank B contains 166 \(\frac{2}{3}\) litres of water.
Check: A = 4 × 166 \(\frac{2}{3}\) = 666 \(\frac{2}{3}\), C = 666 \(\frac{2}{3}\) − 150 = 516 \(\frac{2}{3}\). Total = 166 \(\frac{2}{3}\) + 666 \(\frac{2}{3}\) + 516 \(\frac{2}{3}\) = 1350. ✓