[(6-5x+x^2)/(x^2-16)]/[(x-3)/(4-x)]*[(x^2+5x+4)/(4-x^2)]
=(x-2)(x-3)/(x-4)(x+4)*(4-x)/(x-3)*(x+1)(x+4)/(2+x)(2-x)
=(x+1)/(x+2)
[(6-5x+x^2)/(x^2-16)]/[(x-3)/(4-x)]*[(x^2+5x+4)/(4-x^2)]
=(x-2)(x-3)/(x-4)(x+4)*(4-x)/(x-3)*(x+1)(x+4)/(2+x)(2-x)
=(x+1)/(x+2)