Smita rode her scooty northwards, then turned left, and then again turned left and rode 4 km. She found herself exactly 2 km west of her starting point. How far did she ride northward initially?

She rode 4 km northward at first.

North for a distance, then a left turn faces west, then a left again faces south for 4 km.

Being 2 km west of the start means the final north-south position is level with the start.

So the 4 km south must cancel the initial north distance.

Initial north distance = 4 km.