Question 171488
Fraction {{{(12-4x)/(x^2-1)}}} write as

{{{(-4x+12)/((x-1)(x+1))  =  ((-4)(x-3))/((x-1)(x+1))}}}

Fraction {{{(9-x^2)/(x^2+4x+3)}}} write as

{{{((-1)(x^2-9))/(( x+3)(x+1))}}}  = 
{{{((-1)(x+3)(x-3))/((x+3)(x+1))}}}= {{{((-1)(x-3))/(x+1)}}}

to divide 2 fractions means multiply first by inverse of the second:

{{{((-4)(x-3))/((x-1)(x+1))}}} *  {{{(x+1)/((-1)(x-3))}}}  =  {{{((-4)(x-3)(x+1))/((x-1)(x+1)(-1)(x-3))}}} = {{{4/(x-1)}}}