By what factor would a person’s weight at the surface of Earth change

By what factor would a person’s weight at the surface of Earth change if Earth had its present mass but 8 times its present volume?

In other words, you need to calculate the fraction:

W / W_p = ?
where
w is the new weight of the person,
w_p is the present mass of the person,
under conditions expressed by following two fractions
V / V_p = 8,
M / M_p = 1,
where
V is the new volume of the Earth,
V_p is the present volume of the Earth,
M is the new mass of the Earth,
M_p is the present mass of the Earth.

Solution
Used equations:
V = 4/3 𝜋R³,    R= ¾V^(1/3)/𝜋
W = G mM / R²,

where 

V is the volume of the sphere (the volume of Earth),
R is the radius of the sphere (the radius of Earth),
W is weight of the person,
m is mass of the person,
M is the mass of Earth.
W / Wp = (G mM / R²) / (G mMp / R_p²) = (R_p / R)²
(R_p / R)² = (Vp/V)^2/3 = (1/8)^2/3 = 1/4 = 0.25