​Derive the expression for the force of attraction between two bodies. Define gravitational constant.

Dear Student ,
According to Newton's Law of Gravitation the force of attraction between two bodies with masses m and M with distance between them d is ,$F =\frac{GMm}{d^2}$
Where G is the gravitational constant defined as the force between two objects with which they attract each other per unit mass and the distance between them being unity .
Now the value of G = $6·67\times {10}^{-8} dyne/c{m}^2=6·67\times {10}^{-11}N/m^2$
Regards