Mary starts from her house, walks 80 meters south, and stops to chat with her aunt on the sidewalk. after chatting for a few minutes, she walks 125 meters to the west to meet a friend and then walks 45 meters north with her friend to a café for lunch. overall, she takes 10 minutes to do all of this. what is mary's average speed? a) 8 m/s b) 1.25 m/s c) 25 m/s d) 4.5 e) 0.42