Question

a car travels 60 km to the north of Patna and then 90 km to the south of from there how far from Patna was the car finally

Answer 1

The car first goes 60 km in north direction
that is in plane it goes upwards along y axis
but it finally returns 90km towards south means along - y axis
so the car is finally 30 km south of patna ....

Answer 2

When the car travels 60 km to the north of Patna is is 60 km away from Patna. Again the car comes 90 km to the south of Patna. This time it is 90-60=30 km to the south of Patna.

So , we can say that finally the car is 30 km to the south of Patna.