[tex]\displaystyle\bf\\\frac{x^{2} +6x+9}{3x^{2} +9x} =\frac{x^{2}+2\cdot x\cdot 3+3^{2} }{3x\cdot(x+3)} =\frac{(x+3)^{2} }{3x\cdot(x+3)} =\frac{x+3}{3x}[/tex]