Let the pilot takes off from point A and flies 35 km West t reach B then, it turns South and flies 15 km to reach C, then it turns to its left and flies 20 km eastwards, then it turns north and flies 15 km to finally stop at point E.
⇒ AE =35 - 20 = 15 km ∴ The plane is 15 km west with respect to its starting position.