First of all, it is proved that the escalator is X-class, the speed of my brother is 2v, the time spent by my brother is t 1, the speed spent by my sister is V, the time spent by my sister is t2, and the speed of the elevator is v0.

As for the elevator, my brother * * * takes 100 class, 2vt 1= 100 class, and my sister * * * takes 50 class, so vt2=50, t 1=t2. So I finished it at the same time.

Then, from the ground, they walked the same distance.

That is, 2v-v0 = v+v0, and v = 2v0.

Because 2vt 1= 100, (2v-v0) t1= x.

The two formulas should be divided: x=75.