(a/a-3)-(a+6/a²-3a)+(3/9-a²)
=a/(a-3)-(a+6)/a(a-3)-3/(a-3)(a+3)
=(a³+3a²-a²-9a-18-3a)/a(a-3)(a+3)
=(a³+2a³-12a-18)/a(a-3)(a+3)