This is a problem where you are given the answers and you
want to find the question.  First I'll give you the function,
f(x) = x²-4x-12 and solve it, then show you how to get it: 

x²-4x-12=0
(x-6)(x+2)=0
x-6=0  x+2=0
  x=6    x=-2

Now here's how to get that function.  Just reverse the steps
above and you'll see:

  x=6    x=-2
x-6=0  x+2=0
(x-6)(x+2)=0
x²-4x-12=0

So the function is f(x) = x²-4x-12.

Edwin