coefficient in front of x3 = 3 - 4 = -1.
coefficient in front of x = 7 - 12 = -5.
How did I get that?
First, ask, how many ways you get the form of ax3 if you pick 2 terms and multiply?
First way,3 times x3
Second way, -4x times x2
No other ways.
So the coefficient of x3 = 3 + (-4) = 3 - 4 = -1
You do the coefficient of x one as above too.