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 160 m 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?