Two airliners start from the same airport. A flies 20 km South. B flies 35 km East, then turns South and flies 45 km, then turns to its right and flies 35 km. Where is B with respect to A now?

Let us track the movements of airliner A and airliner B from the origin point (0,0):
Airliner A:

Flies 20 km South → Final position of A =20 km South from origin.

Airliner B:

Flies 35 km East.

Turns South and flies 45 km.

Turns right (towards West) and flies 35 km. This completely cancels out its 35 km East displacement, bringing it back to the same North-South vertical axis line as the origin and A.

Final position of B =45 km South from origin.

Relative Position:
Both A and B lie on the same line going straight South from the origin:

Distance of B with respect to A =45 km−20 km=25 km.

Since B is further down South (45 km) than A (20 km), B is located 25 km South with respect to A.