Your house is located at X and your school is located at Y. Although your school is just opposite but you cannot go straight because of the busy highway in between. So, you first go 125 m due south, then cross a 100 m long subway which is due east and finally reach your school at Y which is 125 m due north. With respect to school at Y your house at X is

The correct answer is 125 m due south.

Let us break down the movement from house X to school Y step by step:

1. Starting from house X, the journey begins by moving 125 m due south to reach the entrance of the subway.
2. Next, crossing the subway involves traveling 100 m due east.
3. Finally, from the subway exit, moving 125 m due north reaches school Y.

To determine the relative location of house X with respect to school Y along the primary vertical directional line:

$\text{Vertical displacement south}=125\text{m}$

Since the initial movement from house X to reach the transverse path towards school Y was directed 125 m towards the south, house X is located 125 m due south relative to school Y.