Thank you for reporting, we will resolve it shortly
Q.
The depth $d$ at which the value of acceleration due to gravity becomes $\frac {1} { n}$ time the value at the surface is (R be the radius of the earth)
At depth d from earth's surface,
$g'=g\left(1-\frac{d}{R} \right)$
Given $g'=\frac{g}{n}$
So, $\frac{g}{n}=g\left(1-\frac{d}{R}\right)$
or $\frac{1}{n}=1-\frac{d}{R}$ or $\frac{d}{R}=1-\frac{1}{n}$
$=\frac{(n-1)R}{n}$
$\therefore $ $d=\frac{(n-1)R}{n}$