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

To simplify the expression, we can combine like terms.

The like terms are the terms that have the same variables raised to the same exponents.

Let's group the like terms together:

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

Now, let's simplify each group of like terms:

(27x³ - 20x³ + 10x³) = 17x³ (- 27x² y + 15x² y + 12x² y) = 0x² y = 0 (9xy² - 4xy² - 5xy²) = 0xy² = 0 (-y³ + 3y³ + y³) = 3y³

Therefore, the simplified expression is:

17x³ + 0 + 0 + 3y³

This can be further simplified to:

17x³ + 3y³