The word 'product' means to multiply, so you're essentially doing -4n(n² - 6n + 3).
To expand the bracket, you multiply -4n by everything inside:
-4n × n² = -4n³
-4n × -6n = 24n²
-4n × 3 = -12n
So all together your answer is -4n³ + 24n² - 12n.
I hope this helps!