(3a+6)/(a²-6a+9)÷(a+2)*(9-a²)/((a+2)(a+3))
=3(a+2)/(a-3)²÷(a+2)*[-(a+3)(a-3)/(a+2)(a+3)]
=3/(a-3)²*[-(a-3)/(a+2)]
=-3/(a+2)(a-3)
=-3/(a²-a-6)
(3a+6)/(a²-6a+9)÷(a+2)*(9-a²)/((a+2)(a+3))
=3(a+2)/(a-3)²÷(a+2)*[-(a+3)(a-3)/(a+2)(a+3)]
=3/(a-3)²*[-(a-3)/(a+2)]
=-3/(a+2)(a-3)
=-3/(a²-a-6)