The given polynomial is,
[tex]3x^6+6x^4+15x^3[/tex]Expand the polynomial.
[tex]3x^3x^3+3\times2x^3x+3\times5x^3[/tex]Take the common factor outside. So, the polynomial in factored form is
[tex]3x^3(x^3+2x+5)[/tex]The term outside the bracket is the GCF.
So, the GCF is ,
[tex]3x^3[/tex]