Weight of an object is directly proportional to the mass of the earth and inversely proportional to the square of the radius of the earth. i.e.
Weight of a body ∝ M/ R2
Original weight Wo = m g = m G (M /R2)
When hypothetically M becomes 4 M and R becomes R /2
then weight becomes Wn= m G (4M/ (R/2)2 = (16 m G) M /R2 = 16 × Wo
The weight will become 16 times.