The answer is B.
Do you need the explanation?
(3x^3 - 7x^2 + 12) - (3x^3 + 6x^2 + 10x)
First, remove parentheses
3x^3 - 7x^2 + 12 - 3x^3 -6x^2 -10x
eliminate the opposites
then collect the like terms
13x^2 +12 - 10x
and finally, use the commutative property to reorder the terms, and you'll get
-13x^2-10x+12
