What is the depth at which the value of acceleration due to gravity...

The value of the acceleration due to gravity when the body moves below the surface of the earth at the depth, $d$ in terms of the radius of the earth, and acceleration due to gravity at the surface of the earth, then at depth:(g_{\text{eff }}=g\left(1-\frac{d}{R}\right) \Rightarrow \frac{g}{n}=g\left(1-\frac{d}{R}\right) \Rightarrow d=\frac{(n-1) R}{n}).