Simplify. (3x^3 - 7x^2 + 12) - (3x^3 + 6x^2 + 10x)

A-x^2 + 10x + 12
B-13x^2 - 10x + 12
C-6x^3 + x^2 - 10x - 12
D-9x^6 - 42x^4 - 10x + 12