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

To simplify the expression, let's combine like terms:

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

Simplifying each term: (27x³ - 20x³ + 10x³) - 27x² y + (15x² y + 12x² y) + (-4xy² - 5xy² + 9xy²) + (y³ + 3y³ + y³)

Combine like terms: 17x³ - 27x² y + 27x² y - 4xy² + 9xy² - 5xy² + y³ + 3y³ + y³

Simplify further: 17x³ - 4xy² + 3xy² + y³ + 3y³ + y³

Combine like terms: 17x³ - xy² + 7y³

So, the simplified expression is 17x³ - xy² + 7y³.