9-16x is the difference of squares and therefore can be factored as:
color(white)("XXXX")9-16x^2 = (3-4x)(3+4x)
color(white)("XXXX")or
color(white)("XXXX")9-16x^2 = (-1)(4x-3)(4x+3)#
So
color(white)("XXXX")(9-16x^2)/(4x-3)
color(white)("XXXX")color(white)("XXXX")= ((-1)cancel((4x-3))(4x+3))/(cancel(4x-3))
color(white)("XXXX")color(white)("XXXX")= -(4x+3)