Riya walked 90 m towards the north from her house, and then took a right turn and walked 60 m to reach the market. Then, she took a left turn and walked a few meters from the market to reach the post office, from where she took a left turn again and walked 160m to reach the school. If the air distance between Riya’s house and the school is 260 m, what is the air distance between the market and the post office?