The force of mutual attraction between any two objects by virtue of their masses is

Let $G, W, E$ and $S$ be the relative strengths of gravitational,weak-nuclear,electromagnetic,and strong-nuclear forces,respectively. Which of the following statements is correct?

Two identical spheres each of radius $r$ are placed in contact with each other. Show that the gravitational force between them is proportional to $r^4$.

Two point masses $m$ and $4m$ are separated by a distance $d$ on a line. $A$ third point mass $m_0$ is to be placed at a point on the line such that the net gravitational force on it is zero. The distance of that point from the $m$ mass is:

Explain the gravitational force exerted by an extended object.

According to Newton's law of gravitation,both the Earth and an apple exert equal forces on each other. Why does the apple fall towards the Earth,but the Earth does not move towards the apple?