Answer:
D
Steps:
Multiply the first term by each term in the second set of parentheses;
3x^2 * 6x = 18x^3
3x^2 * -8 = -24x^2
Now multiply the second term (and third term) by each term in the second set of parentheses;
5x * 6x = 30x^2
5x * -8 = -40x
9 * 6x = 54x
9 * -8 = -72
Then combine all the results;
18x^3 - 24x^2 + 30x^2 - 40x + 54x - 72
And combine like terms;
18x^3 + 6x^2 + 14x - 72
