So you can distribute x and then -4.
Start with x, that would be
x²·x - 2x·x - 3x
x³ - 2x² - 3x
Now distribute -4.
-4x² + 8x + 12
Now put them together:
x³ - 2x² - 3x + (-4x² + 8x + 12)
Combine like terms:
x³ - 6x² + 5x + 12
Final answer: x³ - 6x² + 5x + 12
Hope this helps.