The first polynomial is completely factored; the numbers 121 and 36 don't have a common factor, and the variables are different, so you can't factor them either.
The other three can still be factored:
[tex](4x+4)(x+1)=4(x+1)(x+1)=4(x+1)^{2} [/tex]
[tex]2x( x^{2} -4)=2x(x+2)(x-2)[/tex]
[tex]3 x^{4} -15 n^{3} +12n^{2} =3 x^{4} -n^{2} (15n-12)[/tex]
The correct answer is the first one.
