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/ R^{2}

Original weight W_{o} = m g = m G (M /R^{2})

When hypothetically M becomes 4 M and R becomes R /2

then weight becomes W_{n}= m G (4M/ (R/2)^{2} = (16 m G) M /R^{2 }= 16 × W_{o}

The weight will become 16 times.