The angle of elevation of the summit of a mountain from a point on the ground is $45^{\circ}$. After climbing up one km towards the summit at an inclination of $30^{\circ}$ from the ground, the angle of elevation of the summit is found to be $60^{\circ}$. Then the height (in km) of the summit from the ground is:\\
(1) $\frac{\sqrt{3}-1}{\sqrt{3}+1}$\\
(2) $\frac{\sqrt{3}+1}{\sqrt{3}-1}$\\
(3) $\frac{1}{\sqrt{3}-1}$\\
(4) $\frac{1}{\sqrt{3}+1}$