Answer:
A factor of 2*4 = 8
Explanation:
F_g = (G*m1*m2)/r^2
where m1 and m2 are the two masses, G is Newton's gravitational constant, and r is the distance between the center of mass of the two objects.
So, if you double m1 and quadruple m2:
m1' = 2*m1
m2' = 4*m2
Then F_g' = (G*m1'*m2')/r^2 = (G*2*m1*4*m2)/r^2 = 8*(G*m1*m2)/r^2 = 8*F_g
