the function is:
degree: 4
and we know that some zeros are:
[tex]x=7i,3,-3[/tex]because the function is degree 4 we know that it should have 4 zeros. we also know that the function is symetric because of the real solutions, so the las solution will be the negative of the imaginari root so the remaining zeros are:
[tex]x=-7i[/tex]