The question in the post is posed incorrectly and in this form can not be answered.
To be correct, the question should be changed/edited/modified.
A correct question is "What is the GCF for the terms of polynomial -10x3y4 - 16x5y2?"
Then the answer is GCF = -2x^3y^2.
Firstly, you place into GCF the greatest common factor of integer coefficients -10 and -16, which is -2;
then you place into GCF the greatest common degree of x for both terms, which is x^3;
then you place into GCF the greatest common degree of y for both terms, which is y^2.