The expression for the angle of dip is as follows;
$\delta=\tan ^{-1} \frac{ V }{ H }$
Here, $V$ is the vertical component and $H$ is the horizontal component.
It is given in the problem that at a certain place, horizontal component is equal to the vertical component.
Put $H = V$ in the above expression.
$\delta=\tan ^{-1} \frac{ V }{ H } $
$\delta=\tan ^{-1} \frac{ V }{ V } $
$\delta=\tan ^{-1} 1$
$\delta=45^{\circ}$