27x³ - 27x² y + 9x y² - y³+ 20x³ - 15x² y + 4xy² - 3y³ + 10x³ + 12x² y - 5X y² + y³

To simplify the given expression, let's group like terms and combine them:

27x³ + 20x³ + 10x³ = 57x³ -27x²y - 15x²y + 12x²y = -30x²y 9xy² + 4xy² - 5xy² = 8xy² -y³ - 3y³ + y³ = -3y³

Therefore, the simplified expression is:

57x³ - 30x²y + 8xy² - 3y³