Is it possible to shield a body from a gravitational field?

$(a)$ Prove that if the Earth attracts two bodies placed at the same distance from the center of the Earth with equal force,then their masses will be the same.
$(b)$ Mathematically express the acceleration due to gravity experienced by a free-falling object.
$(c)$ Why is $G$ called a universal gravitational constant?

An object is placed one by one in three liquids having different densities. The object floats with $\frac{1}{9}$, $\frac{2}{11}$, and $\frac{3}{7}$ parts of its volume outside the liquid surface in liquids of densities $d_1$, $d_2$, and $d_3$ respectively. Which of the following statements is correct?

On the Earth,a stone is thrown from a height in a direction parallel to the Earth's surface,while another stone is simultaneously dropped from the same height. Which stone would reach the ground first and why?

Suppose a planet exists whose mass and radius both are half that of Earth. Calculate the acceleration due to gravity on the surface of this planet.

Which is greater: the attraction of earth for $1 \,kg$ of lead or attraction of $1 \,kg$ of lead for earth?