algebra question

h*g =  (4x+1)(-4x+1)  = -16x^2 +1     now put in   x/3   for x

                                   -16x^2/9 +1    and put in a common denominator of 9

                                   (-16x^2 +9 ) / 9    and re-arrange

                                      (9 - 16x² ) / 9