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

To simplify the given expression, we need to combine like terms.

The terms with the same variables raised to the same powers can be combined together.

Let's group the terms accordingly:

27x³ + 20x³ + 10x³ = (27 + 20 + 10)x³ = 57x³ -27x² y - 15x² y + 12x² y = (-27 - 15 + 12)x² y = -30x² y 9x y² + 4xy² - 5X y² = (9 + 4 - 5)xy² = 8xy² -y³ - 3y³ + y³ = (-1 - 3 + 1)y³ = -3y³

Therefore, combining the like terms, we have:

57x³ -30x² y + 8xy² - 3y³