(x-3)／(x+3)^2+x／(3+x)(3-x)
=[(x-3)^2-x(x+3)]／(x+3)^2(x-3)
=(x^2-6x+9-x^2-3x)／(x+3)^2(x-3)
=(-9x+9)／(x+3)^2(x-3)
=9(1-x)／(x+3)^2(x-3)