The last step you would have taken if you were solving a quadratic would
be where you had finished solving for x and had gotten these solutions:

    x=12;   x=2

The last step before that would have been when you had set each factor
equal to 0

  x-12=0;   x-2=0

The last step before that would have been when you had both those factors
multiplied and set equal to 0, so you could use the zero-factor principle:

 (x-12)(x-2)=0

The last step before that would have been before you had factored the
quadratic to get the above.  To undo factoring requires FOIL:

 x²-14x+24=0

That's the quadratic equation you would have begun with.

Edwin