The difference of these two polynomials is the same as the sum of polynomials:
(12x3 – 6x + 4) + (3x2 – 4x – 3)
We distributed the minus sign by flipping every sign in the second polynomial. We flipped them all upside-down too, even though you probably can't tell. We may have gotten a little flip-happy.
We do the new polynomial addition problem and find: