You walk forward at 1.5 m/s for 8s. your friend decides to walk faster and starts out at 2.0 m/s for the first 4 s. then she slows down and walks forward at 1.0 m/s for the next 4s. make a distance-time graph of your motion and your friend's motion. who walked farther?

The first thing you should know is that the distance is equal to the speed per time.
 Therefore if You walk forward at 1.5 m / s for 8s
 d = 1.5t [0,8] s
 Your friend decides to walk faster and starts at 2.0 m / s for the first 4 s.
 d = 2t [0,4] s
 Then she slows down and walks forward at 1.0 m / s for the next 4s
 d = t + 4 [4,8] s
 Who walked farther?
 They both walked the same distance
 12 meters