A man standing at a point P is watching the top of a tower, which makes an angle of elevation of 30º with the man's eye. The man walks some distance towards the tower to watch its top and the angle of the elevation becomes 45º. What is the distance between the base of the tower and the point P?

Answer: Option C

$$\begin{array}{rl}& \tan 45^{\circ }=\frac{SR}{QR}\\ & \tan 30^{\circ }=\frac{SR}{PR}=\frac{SR}{\left(PQ+QR\right)}\end{array}$$
Two equations and 3 variables. Hence we can not find the required value with the given data.

(Note that if one of SR, PQ, QR is known, this becomes two equations and two variables and if that was the case, we could have found out the required value.)