[tex]\Large\boxed{\begin{array}{l}\sf g(-1)=3\cdot(-1)+2=-3+2=-1\\\sf f(g(-1))=(-1)^2-7\cdot (-1)+9\\\sf f(g(-1))=1+7+9=17\\\sf f(1)=1^2-7\cdot1+9=1-7+9=3\\\sf g(f(1))=3\cdot3+2=9+2=11\\\sf f(g(-1))-g(f(1))=17-11=6\\\huge\boxed{\boxed{\boxed{\boxed{\sf\maltese~alternativa~D}}}}\end{array}}[/tex]
